Co-reporter:Sheng Gong and Qian Wang
The Journal of Physical Chemistry C November 9, 2017 Volume 121(Issue 44) pp:24418-24418
Publication Date(Web):October 16, 2017
DOI:10.1021/acs.jpcc.7b07583
Potassium-ion batteries (KIBs), as alternatives to lithium-ion batteries (LIBs), have attracted increasing attention due to the abundance of K in the Earth’s crust. Here, using first-principles calculations, we have found that boron (B)-doped graphene is a promising anode material for KIBs. The studied B4C28 structure has a large specific capacity of 546 mAh/g, a small migration barrier of 0.07 eV, and a moderate potassiation voltage of 0.82 V to suppress the formation of a SEI layer. Moreover, B-doped graphene with a doping concentration of 12.5 at. % is metallic with good electron conductivity that can improve rate performance. Also, B doping makes the substrate electron-deficient and results in significant charge transfer from K to the substrate, thus preventing K atoms from clustering, inhibiting dendrite growth, and leading to a good cycling stability.
Co-reporter:Fancy Qian Wang, Yaguang Guo, Qian Wang, Yoshiyuki Kawazoe, and Puru Jena
Chemistry of Materials November 14, 2017 Volume 29(Issue 21) pp:9300-9300
Publication Date(Web):October 8, 2017
DOI:10.1021/acs.chemmater.7b03279
Using semiclassical Boltzmann transport theory and density functional formalism, we have systematically studied the thermoelectric performance of layered GeAs2. The figure of merit, ZT value, of this layered structure is found to be 2.78 along the out-of-plane direction, with optimal carrier concentration at 800 K. Analysis of the charge density difference and phonon transport properties allows us to attribute such exceptional thermoelectric properties to strong interlayer interaction between the adjacent layers where quasicovalent bonding is responsible for the enhanced electrical conductivity, while the layered structure accounts for the suppressed lattice thermal conductivity. This study highlights the potential of layered crystals for highly efficient thermoelectric materials.
Co-reporter:Sheng Gong, Cunzhi Zhang, Shuo Wang, and Qian Wang
The Journal of Physical Chemistry C May 11, 2017 Volume 121(Issue 18) pp:10258-10258
Publication Date(Web):April 26, 2017
DOI:10.1021/acs.jpcc.7b02826
Transition metal dinitrides (TMDNs) have attracted increasing attention for their rich chemistry, intriguing properties, and potential applications in electronic devices and electrodes. The similarity in atomic ratio with transition-metal dichalcogenide (TMD) sheets leads to an assumption in previous studies that TMDN sheets adopt similar geometry to that of TMD sheets. Here, using global particle-swarm optimization method combined with first-principles calculations, we show a distinct structure of YN2 monolayer containing isolated N2 dimers labeled as O-YN2, which is dynamically, thermally and mechanically stable, and energetically favorable over the previously predicted H- and T-YN2 monolayer structures. Moreover, because of its unique atomic configuration, the O-YN2 sheet is metallic, providing an intrinsic advantage in electrical conductivity over those semiconducting or insulating transition-metal oxides and TMD layers. In particular, we find that O-YN2 is a promising anode material for potassium ion batteries (KIBs) with competitive potassium capacity, low open-circuit voltage, and small migration barrier compared with other anode materials for potassium ion batteries, adding new features to 2D materials family.
Co-reporter:Yaguang Guo, Qian Wang, and Wissam A. Saidi
The Journal of Physical Chemistry C 2017 Volume 121(Issue 3) pp:
Publication Date(Web):January 3, 2017
DOI:10.1021/acs.jpcc.6b11434
Organometal trihalide perovskites are emerging as very promising photovoltaic materials, which is rivaling that of single crystal silicon solar cells despite their polycrystalline nature with relatively high density of grain boundaries (GBs). There is a lack of understanding of the effects of GBs on halide perovskites as their presence in silicon and other photovoltaic materials is generally detrimental to their photovoltaic properties. Using first-principles calculations, we systematically investigate the geometric structures of high-angle tilt GBs in halide perovskites CsPbX3 (X = Cl, Br, and I) starting from the coincidence site lattice model and refining using crystal shifts and lattice expansion. Electronic density of states calculations reveal that GBs in halides perovskites do not generate midgap states because of the large distance between the unsaturated atoms and the atomic reconstructions in the GB region. However, we show that the GBs can induce different very shallow states near the valence band edge that can hinder hole diffusion. We further extend the results to MAPbI3 GBs and also show their benign effect on optoelectronic properties.
Co-reporter:Tianshan Zhao;Dr. Jian Zhou; Qian Wang; Puru Jena
Angewandte Chemie 2017 Volume 129(Issue 43) pp:13606-13610
Publication Date(Web):2017/10/16
DOI:10.1002/ange.201706764
AbstractMultiply charged negative ions are ubiquitous in nature. They are stable as crystals because of charge compensating cations; while in solutions, solvent molecules protect them. However, they are rarely stable in the gas phase because of strong electrostatic repulsion between the extra electrons. Therefore, understanding their stability without the influence of the environment has been of great interest to scientists for decades. While much of the past work has focused on dianions, work on triply charged negative ions is sparse and the search for the smallest trianion that is stable against spontaneous electron emission or fragmentation continues. Stability of BeB11(X)123− (X=CN, SCN, BO) trianions is demonstrated in the gas phase, with BeB11(CN)123− exhibiting colossal stability against electron emission by 2.65 eV and against its neutral adduct by 15.85 eV. The unusual stability of these trianions opens the door to a new class of super-pnictogens with potential applications in aluminum-ion batteries.
Co-reporter:Tianshan Zhao;Dr. Jian Zhou; Qian Wang; Puru Jena
Angewandte Chemie 2017 Volume 129(Issue 43) pp:13333-13333
Publication Date(Web):2017/10/16
DOI:10.1002/ange.201708386
Mehrfach geladene Anionen sind wegen starker elektrostatischer Abstoßung in der Gasphase instabil. Q. Wang, P. Jena et al. beschreiben in der Zuschrift auf S. 13606 das rationale Design der BeB11(X)123−-Trianionen (X=CN, SCN, BO), die in der Gasphase gegen eine spontane Elektronenabgabe um 2.65 eV stabilisiert sind. Bezüglich ihrer chemischen Eigenschaften ähneln die Trianionen den Gruppe-15-Elementen und reagieren selbst mit dem Edelgas Xenon.
Co-reporter:Jie Liu, Tianshan Zhao, Shunhong Zhang, Qian Wang
Nano Energy 2017 Volume 38(Volume 38) pp:
Publication Date(Web):1 August 2017
DOI:10.1016/j.nanoen.2017.05.017
•A new stable 3D metallic carbon, Hex-C18, is identified using global structure search.•Hex-C18 exhibits a large heat capacity, high Debye stiffness, and super hardness.•It is the first time to explore metallic carbon for Li-ion batteries.•Hex-C18 possesses a low Li diffusion energy barrier and a high Li capacity.Metallic carbon has been extensively studied for its potential novel applications in catalysis, superconductivity, and electronic devices. Currently, the design of metallic carbon is mainly by educated intuition which could miss some more stable allotropes. Here we carry out a global structure search on the potential energy surface, and identify a new three-dimensional (3D) metallic carbon phase, termed Hex-C18, which is energetically more favorable than most of the previously identified 3D metallic carbon allotropes. Using state-of-the-art theoretical calculations, we show that Hex-C18 not only possesses a high thermodynamic stability, large heat capacity, high Debye stiffness, anisotropic elasticity, and super hardness, but also is a promising anode material for lithium ion batteries (LIBs). As compared to graphite commercially used in LIBs, Hex-C18 exhibits a lower Li diffusion energy barrier and a higher Li capacity because of its intrinsic metallicity and regular porosity. In addition, the simulated x-ray diffraction of Hex-C18 matches well with a previously unidentified low-angle diffraction peak in experimental XRD spectra of detonation soot, implying the possibility of its existence in the specimen. This study expands the family of metallic carbon, and may open a new frontier in design of high performance anode materials for LIBs as well.Download high-res image (380KB)Download full-size image
Co-reporter:Tianshan Zhao;Puru Jena
Nanoscale (2009-Present) 2017 vol. 9(Issue 15) pp:4891-4897
Publication Date(Web):2017/04/13
DOI:10.1039/C7NR00227K
Super-alkalis are clusters of atoms. With ionization potentials smaller than those of the alkali atoms, they are playing an increasing role in chemistry as highlighted by recent applications in solar cells as well as in Li-ion batteries. For the past 40 years superalkalis were designed using inorganic elements with the sp orbital character. Here, we show that a large class of superalkalis composed of only simple metal atoms, transition metal complexes as well as organic molecules can be designed by making use of electron counting rules beyond the octet rule. Examples include Al3+, Mn(B3N3H6)2+, B9C3H12+, and C5NH6+ which obey the jellium shell closure rule, the 18-electron rule, the Wade–Mingos rule, and Hückel's aromatic rule, respectively. We further show that the ability of superalkalis to transfer an electron easily can be used to activate a CO2 molecule by transforming it from a linear to a bent structure. These results, based on density functional theory with generalized gradient approximation for exchange–correlation potential, open the door to a new class of catalysts for CO2 activation.
Co-reporter:Xiaoyin Li;Shunhong Zhang
Nanoscale (2009-Present) 2017 vol. 9(Issue 2) pp:562-569
Publication Date(Web):2017/01/05
DOI:10.1039/C6NR07851F
First-principles calculations and extensive analyses reveal that the H phase of two-dimensional (2D) transition metal dichalcogenides (TMDs) can be tuned to topological insulators by introducing square–octagon (4–8) defects and by applying equi-biaxial tensile strain simultaneously. The 2D structure composed of hexagonal rings with 4–8 defects, named sho-TMD, is dynamically and thermally stable. The critical equi-biaxial tensile strain for the topological phase transition is 4%, 6%, and 4% for sho-MoS2, sho-MoSe2 and sho-WS2, respectively, and the corresponding nontrivial band gap induced by the spin–orbit coupling is 2, 8, and 22 meV, implying the possibility of observing the helical conducting edge states that are free of backscattering in experiment. It is equally interesting that the size of the energy band gap of the H-phase can be flexibly tuned by changing the concentration of 4–8 defects while the feature of the quasi-direct band gap semiconductor remains. These findings add additional traits to the TMD family, and provide a new strategy for engineering the electronic structure and the band topology of 2D TMDs for applications in nanoelectronics and spintronics.
Co-reporter:Tianshan Zhao, Shunhong Zhang, Yaguang Guo and Qian Wang
Nanoscale 2016 vol. 8(Issue 1) pp:233-242
Publication Date(Web):15 Oct 2015
DOI:10.1039/C5NR04472C
MXenes are attracting attention due to their rich chemistry and intriguing properties. Here a new type of metal–carbon-based sheet composed of transition metal centers and C2 dimers rather than individual C atom is designed. Taking the Ti system as a test case, density functional theory calculations combined with a thermodynamic analysis uncover the thermal and dynamic stability of the sheet, as well as a metallic band structure, anisotropic Young's modulus and Poisson's ratio, a high heat capacity, and a large Debye stiffness. Moreover, the TiC2 sheet has an excellent Li storage capacity with a small migration barrier, a lower mass density compared with standard MXenes, and better chemical stability as compared to the MXene Ti2C sheet. When Ti is replaced with other transition metal centers, diverse new MC2 sheets containing CC dimers can be formed, the properties of which merit further investigation.
Co-reporter:Yaguang Guo, Shunhong Zhang, Tianshan Zhao and Qian Wang
Nanoscale 2016 vol. 8(Issue 20) pp:10598-10606
Publication Date(Web):22 Dec 2015
DOI:10.1039/C5NR06788J
Mechanical cleavage, chemical intercalation and chemical vapor deposition are the main methods that are currently used to synthesize nanosheets or monolayers. Here, we propose a new strategy, thermal exfoliation for the fabrication of silica monolayers. Using a variety of state-of-the-art theoretical calculations we show that a stoichiometric single-layer silica with a tetragonal lattice, T-silica, can be thermally exfoliated from the stishovite phase in a clean environment at room temperature. The resulting single-layer silica is dynamically, thermally, and mechanically stable with exceptional properties, including a large band gap of 7.2 eV, an unusual negative Poisson's ratio, a giant Stark effect, and a high breakdown voltage. Moreover, other analogous structures like single-layer GeO2 can also be obtained by thermal exfoliation of its bulk phase. Our findings are expected to motivate experimental efforts on developing new techniques for the synthesis of monolayer materials.
Co-reporter:Tianshan Zhao, Jian Zhou, Qian Wang, Yoshiyuki Kawazoe, and Puru Jena
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 39) pp:26207
Publication Date(Web):September 13, 2016
DOI:10.1021/acsami.6b07482
Ferromagnetism and half-metallicity are two vital properties of a material for realizing its potential in spintronics applications. However, none of the two-dimensional (2D) pristine metal–carbide sheets synthesized experimentally exhibits half-metallicity with ferromagnetic coupling. Here, a ferromagnetic and half-metallic FeC2 sheet containing isolated C2 dimers rather than individual carbon atoms is predicted to be such a material. Based on state-of-the-art theoretical calculations, we show that the FeC2 sheet is dynamically, thermally, and mechanically stable and can be chemically exfoliated from the bulk phase of layered ThFeC2. Due to its unique atomic configuration, the FeC2 sheet exhibits ferromagnetism with a Curie temperature of 245 K. This is in contrast to its bulk counterpart, ThFeC2, which is paramagnetic. We also find that, unlike the metallic metal–carbide sheets, the FeC2 sheet is half-metallic with semiconducting spin-up and metallic spin-down channels. Moreover, half-metallicity can remain until an equi-biaxial strain of 10%. In addition, we provide the Raman and infrared spectra which can be used to identify this new 2D structure experimentally in the future.Keywords: C2 dimer; electronic structure; FeC2 monolayer; ferromagnetism; half-metallicity
Co-reporter:Fancy Qian Wang, Jiabing Yu, Qian Wang, Yoshiyuki Kawazoe, Puru Jena
Carbon 2016 Volume 105() pp:424-429
Publication Date(Web):August 2016
DOI:10.1016/j.carbon.2016.04.054
Motivated by the unique geometry and novel properties of penta-graphene proposed recently as a new carbon allotrope consisting of pure pentagons [Zhang et al. Proc. Natl. Acad. Sci. 2015, 112, 2372], we systematically investigated its phonon transport properties by solving exactly the linearized phonon Boltzmann transport equation combined with first principles calculations. The intrinsic lattice thermal conductivity Klat of penta-graphene is found to be about 645 W/mK at room temperature, which is significantly reduced as compared to that of graphene. The underlying reason is the strong anharmonic effect introduced by the buckled pentagonal structure with hybridized sp2 and sp3 bonding. A detailed analysis of the phonons of penta-graphene reveals that the ZA mode is the primary heat carrier (nearly 60%). The Klat is dominated by three-phonon scattering where the scattering rate of the Normal scattering process is comparable to that of the Umklapp scattering process. The phonon mean free path of the collective phonon excitations is in the order of micrometers. Complementing the high thermal conductivity of graphene, the low thermal conductivity of penta-graphene adds additional features to the family of carbon materials for thermal applications.
Co-reporter:Xiaoyin Li, Shunhong Zhang, Fancy Qian Wang, Yaguang Guo, Jie Liu and Qian Wang
Physical Chemistry Chemical Physics 2016 vol. 18(Issue 21) pp:14191-14197
Publication Date(Web):30 Mar 2016
DOI:10.1039/C6CP01092J
Penta-graphene has recently been proposed as a new allotrope of carbon composed of pure pentagons, and displays many novel properties going beyond graphene [Zhang et al., Proc. Natl. Acad. Sci. U. S. A., 2015, 112, 2372]. To further explore the property modulations, we have carried out a theoretical investigation of the hydrogenated and fluorinated penta-graphene sheets. Our first-principles calculations reveal that hydrogenation and fluorination can effectively tune the electronic and mechanical properties of penta-graphene: turning the sheet from semiconducting to insulating; changing the Poisson's ratio from negative to positive, and reducing the Young's modulus. Moreover, the band gaps of the hydrogenated and fluorinated penta-graphene sheets are larger than those of fully hydrogenated and fluorinated graphene by 0.37 and 0.04 eV, respectively. The phonon dispersions and ab initio molecular dynamics simulations confirm that the surface modified penta-graphene sheets are dynamically and thermally stable, and show that the hydrogenated penta-graphene has more Raman-active modes with higher frequencies as compared to the fluorinated penta-graphene.
Co-reporter:Tianshan Zhao; Jian Zhou; Qian Wang;Puru Jena
The Journal of Physical Chemistry Letters 2016 Volume 7(Issue 14) pp:2689-2695
Publication Date(Web):June 28, 2016
DOI:10.1021/acs.jpclett.6b00981
Using multiscale first-principles calculations, we show that two interacting negatively charged B12I9– monoanions not only attract, in defiance of the Coulomb’s law, but also the energy barrier at 400 K is small enough that these two moieties combine to form a stable B24I182– moiety. Ab initio molecular dynamics simulations further confirm its stability up to 1500 K. Studies of other B12X9– (X = Br, Cl, F, H, Au, CN) show that while all of these B24X182– moieties are stable against dissociation, the energy barrier, with the exception of B24Au182–, is large so as to hinder their experimental observation. Our results explain the recent experimental observation of the “spontaneous” formation of B24I182– in an ion trap. A simple model based upon electrostatics shows that this unusual behavior is due to competition between the attractive dipole–dipole interaction caused by the aspherical shape of the particle and the repulsive interaction between the like charges.
Co-reporter:Shunhong Zhang
The Journal of Physical Chemistry C 2016 Volume 120(Issue 7) pp:3993-3998
Publication Date(Web):January 28, 2016
DOI:10.1021/acs.jpcc.5b12510
Using first-principles calculations combined with ab initio molecular dynamics and tight binding model, we predict the existence of a kinetically stable two-dimensional (2D) penta-CN2 sheet, which is isostructural to the recently discovered penta-graphene. The concentration of N in this new carbon nitride sheet exceeds the maximum N content, namely 21.66%, that has been achieved experimentally in honeycomb geometry. It even exceeds the N content found recently in hole-doped carbon nitride C0.5N0.5 as well as in porous graphitic C3N4. The penta-CN2 sheet contains N–N single bonds with an energy density of 4.41 kJ/g, higher than that predicted recently in nitrogen-rich B–N compound. Remarkably, penta-CN2 has an in-plane axial Young’s modulus of 319 N/m, even stiffer than the h-BN monolayer. The electronic band structure of penta-CN2 exhibits an interesting double degeneracy at the first Brillouin zone edges which is protected by the nonsymmorphic symmetry and can be found in other isostructural chemical analogues. The band gap of penta-CN2 calculated using HSE06 functional is 6.53 eV, suggesting its insulating nature. The prediction of a stable penta-CN2 implies that puckering might be more effective than porosity in holding nitrogen in 2D carbon nitrides. This sheds new light on how to design nitrogen-rich C–N compounds beyond N-doped graphene.
Co-reporter:Ke-Wei Ding, Xiao-Wei Li, Hong-Guang Xu, Tao-Qi Li, Zhong-Xue Ge, Qian Wang and Wei-Jun Zheng
Chemical Science 2015 vol. 6(Issue 8) pp:4723-4729
Publication Date(Web):11 May 2015
DOI:10.1039/C5SC01103E
TiNn+ clusters were generated by laser ablation and analyzed experimentally by mass spectrometry. The results showed that the mass peak of the TiN12+ cluster is dominant in the spectrum. The TiN12+ cluster was further investigated by photodissociation experiments with 266, 532 and 1064 nm photons. Density functional calculations were conducted to investigate stable structures of TiN12+ and the corresponding neutral cluster, TiN12. The theoretical calculations found that the most stable structure of TiN12+ is Ti(N2)6+ with Oh symmetry. The calculated binding energy is in good agreement with that obtained from the photodissociation experiments. The most stable structure of neutral TiN12 is Ti(N2)6 with D3d symmetry. The Ti–N bond strengths are greater than 0.94 eV in both Ti(N2)6+ and its neutral counterpart. The interaction between Ti and N2 weakens the N–N bond significantly. For neutral TiN12, the Ti(N3)4 azide, the N5TiN7 sandwich structure and the N6TiN6 structure are much higher in energy than the Ti(N2)6 complex. The DFT calculations predicted that the decomposition of Ti(N3)4, N5TiN7, and N6TiN6 into a Ti atom and six N2 molecules can release energies of about 139, 857, and 978 kJ mol−1 respectively.
Co-reporter:Fancy Qian Wang, Shunhong Zhang, Jiabing Yu and Qian Wang
Nanoscale 2015 vol. 7(Issue 38) pp:15962-15970
Publication Date(Web):25 Aug 2015
DOI:10.1039/C5NR03813H
Motivated by the recent study of inspiring thermoelectric properties in bulk SnSe [Zhao et al., Nature, 2014, 508, 373] and the experimental synthesis of SnSe sheets [Chen et al., J. Am. Chem. Soc., 2013, 135, 1213], we have carried out systematic calculations for a single-layered SnSe sheet focusing on its stability, electronic structure and thermoelectric properties by using density functional theory combined with Boltzmann transport theory. We have found that the sheet is dynamically and thermally stable with a band gap of 1.28 eV, and the figure of merit (ZT) reaches 3.27 (2.76) along the armchair (zigzag) direction with optimal n-type carrier concentration, which is enhanced nearly 7 times compared to its bulk counterpart at 700 K due to quantum confinement effect. Furthermore, we designed four types of thermoelectric couples by assembling single-layered SnSe sheets with different transport directions and doping types, and found that their efficiencies are all above 13%, which are higher than those of thermoelectric couples made of commercial bulk Bi2Te3 (7%–8%), suggesting the great potential of single-layered SnSe sheets for heat-electricity conversion.
Co-reporter:Shunhong Zhang;Puru Jena;Jian Zhou;Xiaoshuang Chen;Yoshiyuki Kawazoe
PNAS 2015 Volume 112 (Issue 8 ) pp:2372-2377
Publication Date(Web):2015-02-24
DOI:10.1073/pnas.1416591112
A 2D metastable carbon allotrope, penta-graphene, composed entirely of carbon pentagons and resembling the Cairo pentagonal
tiling, is proposed. State-of-the-art theoretical calculations confirm that the new carbon polymorph is not only dynamically
and mechanically stable, but also can withstand temperatures as high as 1000 K. Due to its unique atomic configuration, penta-graphene
has an unusual negative Poisson’s ratio and ultrahigh ideal strength that can even outperform graphene. Furthermore, unlike
graphene that needs to be functionalized for opening a band gap, penta-graphene possesses an intrinsic quasi-direct band gap
as large as 3.25 eV, close to that of ZnO and GaN. Equally important, penta-graphene can be exfoliated from T12-carbon. When
rolled up, it can form pentagon-based nanotubes which are semiconducting, regardless of their chirality. When stacked in different
patterns, stable 3D twin structures of T12-carbon are generated with band gaps even larger than that of T12-carbon. The versatility
of penta-graphene and its derivatives are expected to have broad applications in nanoelectronics and nanomechanics.
Co-reporter:Jie Liu
The Journal of Physical Chemistry C 2015 Volume 119(Issue 43) pp:24674-24680
Publication Date(Web):October 7, 2015
DOI:10.1021/acs.jpcc.5b08593
In all of the phosphorus monolayers reported to date, phosphorus is 3-fold coordinated. However, flexible chemistry of phosphorus allows it to have varying coordination number up to 6. Here, we report three new phosphorus monolayers (labeled α-P6, β-P6, and 558-P6) having 2-, 3-, and 4-fold coordination, which can be observed in epitaxial growth where flakes merge forming ridges at the boundaries. On the basis of state-of-the-art theoretical simulations, we show that these three new monolayer allotropes are thermally and dynamically stable, and they have comparable energetic stability with some reported monolayers such as δ-P, γ-P, and ε-P. Because of their special atomic configurations, they exhibit exceptional properties, including extremely high electron mobility, anisotropic Young’s moduli, and optical absorbance in visible and ultraviolet regions. These findings can extend the family of phosphorenes with novel properties and potential for applications.
Co-reporter:Yaguang Guo, Shunhong Zhang and Qian Wang
Physical Chemistry Chemical Physics 2014 vol. 16(Issue 31) pp:16832-16836
Publication Date(Web):13 Jun 2014
DOI:10.1039/C4CP01491J
Si based sheets have attracted tremendous attention due to their compatibility with the well-developed Si-based semiconductor industry. On the basis of state-of-the-art theoretical calculations, we systematically study the stability, electronic and optical properties of Si based porous sheets including g-Si4N3, g-Si3N4, g-Si3N3 and g-Si3P3. We find that the g-Si3N3 and g-Si3P3 sheets are thermally stable, while the g-Si4N3 and g-Si3N4 are unstable. Different from the silicene-like sheets of SiN and Si3N which are nonplanar and metallic, both the porous g-Si3N3 and g-Si3P3 sheets are planar and nonmetallic, and the former is an indirect band gap semiconductor with a band gap of 3.50 eV, while the latter is a direct band gap semiconductor with a gap of 1.93 eV. Analysis of the optical absorption spectrum reveals that the g-Si3P3 sheet may have applications in solar absorbers owing to its narrow direct band gap and wide range optical absorption in the visible light spectrum.
Co-reporter:Tianshan Zhao, Shunhong Zhang, Qian Wang, Yoshiyuki Kawazoe and Puru Jena
Physical Chemistry Chemical Physics 2014 vol. 16(Issue 42) pp:22979-22986
Publication Date(Web):07 Aug 2014
DOI:10.1039/C4CP02758B
Due to its compatibility with the well-developed Si-based semiconductor industry, silicene has attracted considerable attention. Using density functional theory we show for the first time that the recently synthesized superhalogen MnCl3 can be used to tune the electronic and magnetic properties of silicene, from semi-metallic to semiconducting with a wide range of band gaps, as well as from nonmagnetic to ferromagnetic (or antiferromagnetic) by changing the coverage of the superhalogen molecules. The electronic properties can be further modulated when a superhalogen and a halogen are used synergistically. The present study indicates that because of the large electron affinity and rich structural diversity superhalogen molecules have advantages over the conventional halogen atoms in modulating the material properties of silicene.
Co-reporter:Shunhong Zhang ; Qian Wang ; Yoshiyuki Kawazoe ;Puru Jena
Journal of the American Chemical Society 2013 Volume 135(Issue 48) pp:18216-18221
Publication Date(Web):November 5, 2013
DOI:10.1021/ja410088y
Boron nitride (BN) and carbon are chemical analogues of each other and share similar structures such as one-dimensional nanotubes, two-dimensional nanosheets characterized by sp2 bonding, and three-dimensional diamond structures characterized by sp3 bonding. However, unlike carbon which can be metallic in one, two, and three dimensions, BN is an insulator, irrespective of its structure and dimensionality. On the basis of state-of-the-art theoretical calculations, we propose a tetragonal phase of BN which is both dynamically stable and metallic. Analysis of its band structure, density of states, and electron localization function confirms the origin of the metallic behavior to be due to the delocalized B 2p electrons. The metallicity exhibited in the studied three-dimensional BN structures can lead to materials beyond conventional ceramics as well as to materials with potential for applications in electronic devices.
Co-reporter:Xiaowei Li, Shunhong Zhang and Qian Wang
Physical Chemistry Chemical Physics 2013 vol. 15(Issue 19) pp:7142-7146
Publication Date(Web):04 Apr 2013
DOI:10.1039/C3CP44660C
Due to their porosity and biocompatibility, C–N based graphitic sheets are currently attracting much attention. Here we present our findings on a new structure of a g-C4N3 sheet composed of the tri-ring heptazine-like units, which is energetically more stable, more elastic and isotropic than the previously proposed structure consisting of the single-ring triazines. Dynamics and thermal stability of the new structure are confirmed using phonon spectrum calculations and molecular dynamics simulations. Based on hybrid density functional theory, we demonstrate that the tri-ring unit based g-C4N3 is a semiconductor with a small band gap, sharp optical absorption peaks and high absorption intensity. Although the new structure is nonmagnetic, ferromagnetism can be introduced and the optical absorption can be tuned by applying a small strain.
Co-reporter:Tianshan Zhao;Yawei Li; Qian Wang; Puru Jena
ChemPhysChem 2013 Volume 14( Issue 14) pp:3227-3232
Publication Date(Web):
DOI:10.1002/cphc.201300511
Abstract
Owing to their s2p5 electronic configuration, halogen atoms are highly electronegative and constitute the anionic components of salts. Whereas clusters that contain no halogen atoms, such as AlH4, mimic the chemistry of halogens and readily form salts (e.g., Na+(AlH4)−), clusters that are solely composed of metal atoms and yet behave in the same manner as a halogen are rare. Because coinage-metal atoms (Cu, Ag, and Au) only have one valence electron in their outermost electronic shell, as in H, we examined the possibility that, on interacting with Al, in particular as AlX4 (X=Cu, Ag, Au), these metal atoms may exhibit halogen-like properties. By using density functional theory, we show that AlAu4 not only mimics the chemistry of halogens, but also, with a vertical detachment energy (VDE) of 3.98 eV in its anionic form, is a superhalogen. Similarly, analogous to XHX superhalogens (X=F, Cl, Br), XAuX species with VDEs of 4.65, 4.50, and 4.34 eV in their anionic form, respectively, also form superhalogens. In addition, Au can also form hyperhalogens, a recently discovered species that show electron affinities (EAs) that are even higher than those of their corresponding superhalogen building blocks. For example, the VDEs of M(AlAu4)2− (M=Na and K) and anionic (FAuF)Au(FAuF) range from 4.06 to 5.70 eV. Au-based superhalogen anions, such as AlAu4− and AuF2−, have the additional advantage that they exhibit wider optical absorption ranges than their H-based analogues, AlH4− and HF2−. Because of the catalytic properties and the biocompatibility of Au, Au-based superhalogens may be multifunctional. However, similar studies that were carried out for Cu and Ag atoms have shown that, unlike AlAu4, AlX4 (X=Cu, Ag) clusters are not superhalogens, a property that can be attributed to the large EA of the Au atom.
Co-reporter:Tianshan Zhao;Yawei Li; Qian Wang; Puru Jena
ChemPhysChem 2013 Volume 14( Issue 14) pp:
Publication Date(Web):
DOI:10.1002/cphc.201390067
Co-reporter:Shunhong Zhang ; Jian Zhou ; Qian Wang ;Puru Jena
The Journal of Physical Chemistry C 2013 Volume 117(Issue 2) pp:1064-1070
Publication Date(Web):January 8, 2013
DOI:10.1021/jp310895q
The recent success in synthesizing graphene monoxide (GMO) with rigorous stoichiometric ratio C:O = 1:1 has highlighted the need to determine its ground state geometry and to explore its physical properties. Using density functional theory and molecular dynamics simulation, we have found a new ether-type configuration of the GMO that is not only lower in energy than any other structures reported thus far, but is also stable up to 2000 K at which previous reported structures dissociate into CO molecules. The dynamic stability of the structure is further confirmed by calculating its phonon spectra. Furthermore, this ether-type structure exhibits anisotropies in mechanical stiffness and in electronic transport. Band gap, carrier concentration, and effective mass can be sensitively modulated by strain or higher oxidation level with C:O = 1:2. This study provides new theoretical insights into geometry, stability, and properties of the hotly pursued graphene oxide with unprecedented applications.
Co-reporter:Xiaowei Li, Jian Zhou, Qian Wang, Yushiyuki Kawazoe, and Puru Jena
The Journal of Physical Chemistry Letters 2013 Volume 4(Issue 2) pp:259-263
Publication Date(Web):December 26, 2012
DOI:10.1021/jz3018804
We propose porous C–N-based structures for biocompatible magnetic materials that do not contain even a single metal ion. Using first-principles calculations based on density functional theory, we show that when patterned in the form of a kagome lattice, nonmagnetic g-C3N4 not only becomes ferromagnetic but also its magnetic properties can be further enhanced by applying external strain. Similarly, the magnetic moment per atom in ferromagnetic g-C4N3 is increased three fold when patterned into a kagome lattice. The Curie temperature of g-C3N4 kagome lattice is 100 K, while that of g-C4N3 kagome lattice is much higher, namely, 520 K. To date, all of the synthesized two- and three-dimensional magnetic kagome structures contain metal ions and are toxic. The objective of our work is to stimulate an experimental effort to develop nanopatterning techniques for the synthesis of g-C3N4- and g-C4N3-based kagome lattices.Keywords: graphitic material; kagome lattice; magnetism; nanopatterning; single atomic porous sheet;
Co-reporter:Xiaowei Li and Qian Wang
Physical Chemistry Chemical Physics 2012 vol. 14(Issue 6) pp:2065-2069
Publication Date(Web):10 Jan 2012
DOI:10.1039/C2CP22997H
Triangular graphene nanoflakes (TGFs), due to their novel magnetic configurations, can serve as building blocks to design new magnetic materials. Based on spin polarized density functional theory, we show that the two dimensional (2D) structures composed of zigzag-edged TGFs linked by 1,3,5-benzenetriyl units (TGFN–C6H3) are ferromagnetic. Their magnetic moments can be tuned by changing the size and edge termination of TGFs, namely magnetic moments increase linearly with the size of TGFs, and double hydrogenation of the edge carbon atoms can significantly enhance stability of the ferromagnetic states. The dynamic stability of the assembled 2D structures is further confirmed by frequency calculations. The characteristic breathing mode is identified where the frequency changes with the inverse square root of the TGFs width, which can be used to identify the size of TGFN–C6H3 in Raman experiments. This study provides new pathways to assemble 2D ferromagnetic carbon materials.
Co-reporter:Xiaowei Li ; Qian Wang ;Puru Jena
The Journal of Physical Chemistry C 2011 Volume 115(Issue 40) pp:19621-19625
Publication Date(Web):September 16, 2011
DOI:10.1021/jp206667r
Development of organic materials with novel magnetic properties has been an important and challenging topic in organic chemistry. A useful paradigm in this direction is to have spin-containing (SC) components linked by ferromagnetic coupling (FC) units. Compared with the traditional SC components such as poly(1,3-phenylenecarbene)s and poly(1,3-phenylenephenylmethine)s, we show that the atomic carbon chains, due to their inherent magnetism and structural simplicity, can be promising magnetic building blocks of 2-D magnetic carbon structures. Using calculations based on density functional theory, we show that the structures constructed by the carbon chains with an odd number of C atoms linked by 1,3,5-benzenetriyl units are ferromagnetic. Independent of the chain length, each structural unit cell has a magnetic moment of 6.0μB and couples ferromagnetically in the 2-D lattice, although the energy difference between the ferromagnetic and antiferromagnetic coupling decreases with increasing chain length. The dynamic stability of the structures is confirmed by frequency calculations. The middle and high vibrational frequencies corresponding to the A1g and E2g modes of the structures with odd number carbon chains lie in the range of 950–1470 cm–1, which are lower than those (980 and 1555 cm–1) with even-numbered carbon chain structures. This suggests that Raman spectra can be used to identify the parity of carbon chains.
Co-reporter:Xiaowei Li, Shunhong Zhang and Qian Wang
Physical Chemistry Chemical Physics 2013 - vol. 15(Issue 19) pp:NaN7146-7146
Publication Date(Web):2013/04/04
DOI:10.1039/C3CP44660C
Due to their porosity and biocompatibility, C–N based graphitic sheets are currently attracting much attention. Here we present our findings on a new structure of a g-C4N3 sheet composed of the tri-ring heptazine-like units, which is energetically more stable, more elastic and isotropic than the previously proposed structure consisting of the single-ring triazines. Dynamics and thermal stability of the new structure are confirmed using phonon spectrum calculations and molecular dynamics simulations. Based on hybrid density functional theory, we demonstrate that the tri-ring unit based g-C4N3 is a semiconductor with a small band gap, sharp optical absorption peaks and high absorption intensity. Although the new structure is nonmagnetic, ferromagnetism can be introduced and the optical absorption can be tuned by applying a small strain.
Co-reporter:Tianshan Zhao, Shunhong Zhang, Qian Wang, Yoshiyuki Kawazoe and Puru Jena
Physical Chemistry Chemical Physics 2014 - vol. 16(Issue 42) pp:NaN22986-22986
Publication Date(Web):2014/08/07
DOI:10.1039/C4CP02758B
Due to its compatibility with the well-developed Si-based semiconductor industry, silicene has attracted considerable attention. Using density functional theory we show for the first time that the recently synthesized superhalogen MnCl3 can be used to tune the electronic and magnetic properties of silicene, from semi-metallic to semiconducting with a wide range of band gaps, as well as from nonmagnetic to ferromagnetic (or antiferromagnetic) by changing the coverage of the superhalogen molecules. The electronic properties can be further modulated when a superhalogen and a halogen are used synergistically. The present study indicates that because of the large electron affinity and rich structural diversity superhalogen molecules have advantages over the conventional halogen atoms in modulating the material properties of silicene.
Co-reporter:Ke-Wei Ding, Xiao-Wei Li, Hong-Guang Xu, Tao-Qi Li, Zhong-Xue Ge, Qian Wang and Wei-Jun Zheng
Chemical Science (2010-Present) 2015 - vol. 6(Issue 8) pp:NaN4729-4729
Publication Date(Web):2015/05/11
DOI:10.1039/C5SC01103E
TiNn+ clusters were generated by laser ablation and analyzed experimentally by mass spectrometry. The results showed that the mass peak of the TiN12+ cluster is dominant in the spectrum. The TiN12+ cluster was further investigated by photodissociation experiments with 266, 532 and 1064 nm photons. Density functional calculations were conducted to investigate stable structures of TiN12+ and the corresponding neutral cluster, TiN12. The theoretical calculations found that the most stable structure of TiN12+ is Ti(N2)6+ with Oh symmetry. The calculated binding energy is in good agreement with that obtained from the photodissociation experiments. The most stable structure of neutral TiN12 is Ti(N2)6 with D3d symmetry. The Ti–N bond strengths are greater than 0.94 eV in both Ti(N2)6+ and its neutral counterpart. The interaction between Ti and N2 weakens the N–N bond significantly. For neutral TiN12, the Ti(N3)4 azide, the N5TiN7 sandwich structure and the N6TiN6 structure are much higher in energy than the Ti(N2)6 complex. The DFT calculations predicted that the decomposition of Ti(N3)4, N5TiN7, and N6TiN6 into a Ti atom and six N2 molecules can release energies of about 139, 857, and 978 kJ mol−1 respectively.
Co-reporter:Xiaowei Li and Qian Wang
Physical Chemistry Chemical Physics 2012 - vol. 14(Issue 6) pp:NaN2069-2069
Publication Date(Web):2012/01/10
DOI:10.1039/C2CP22997H
Triangular graphene nanoflakes (TGFs), due to their novel magnetic configurations, can serve as building blocks to design new magnetic materials. Based on spin polarized density functional theory, we show that the two dimensional (2D) structures composed of zigzag-edged TGFs linked by 1,3,5-benzenetriyl units (TGFN–C6H3) are ferromagnetic. Their magnetic moments can be tuned by changing the size and edge termination of TGFs, namely magnetic moments increase linearly with the size of TGFs, and double hydrogenation of the edge carbon atoms can significantly enhance stability of the ferromagnetic states. The dynamic stability of the assembled 2D structures is further confirmed by frequency calculations. The characteristic breathing mode is identified where the frequency changes with the inverse square root of the TGFs width, which can be used to identify the size of TGFN–C6H3 in Raman experiments. This study provides new pathways to assemble 2D ferromagnetic carbon materials.
Co-reporter:Xiaoyin Li, Shunhong Zhang, Fancy Qian Wang, Yaguang Guo, Jie Liu and Qian Wang
Physical Chemistry Chemical Physics 2016 - vol. 18(Issue 21) pp:NaN14197-14197
Publication Date(Web):2016/03/30
DOI:10.1039/C6CP01092J
Penta-graphene has recently been proposed as a new allotrope of carbon composed of pure pentagons, and displays many novel properties going beyond graphene [Zhang et al., Proc. Natl. Acad. Sci. U. S. A., 2015, 112, 2372]. To further explore the property modulations, we have carried out a theoretical investigation of the hydrogenated and fluorinated penta-graphene sheets. Our first-principles calculations reveal that hydrogenation and fluorination can effectively tune the electronic and mechanical properties of penta-graphene: turning the sheet from semiconducting to insulating; changing the Poisson's ratio from negative to positive, and reducing the Young's modulus. Moreover, the band gaps of the hydrogenated and fluorinated penta-graphene sheets are larger than those of fully hydrogenated and fluorinated graphene by 0.37 and 0.04 eV, respectively. The phonon dispersions and ab initio molecular dynamics simulations confirm that the surface modified penta-graphene sheets are dynamically and thermally stable, and show that the hydrogenated penta-graphene has more Raman-active modes with higher frequencies as compared to the fluorinated penta-graphene.
Co-reporter:Yaguang Guo, Shunhong Zhang and Qian Wang
Physical Chemistry Chemical Physics 2014 - vol. 16(Issue 31) pp:NaN16836-16836
Publication Date(Web):2014/06/13
DOI:10.1039/C4CP01491J
Si based sheets have attracted tremendous attention due to their compatibility with the well-developed Si-based semiconductor industry. On the basis of state-of-the-art theoretical calculations, we systematically study the stability, electronic and optical properties of Si based porous sheets including g-Si4N3, g-Si3N4, g-Si3N3 and g-Si3P3. We find that the g-Si3N3 and g-Si3P3 sheets are thermally stable, while the g-Si4N3 and g-Si3N4 are unstable. Different from the silicene-like sheets of SiN and Si3N which are nonplanar and metallic, both the porous g-Si3N3 and g-Si3P3 sheets are planar and nonmetallic, and the former is an indirect band gap semiconductor with a band gap of 3.50 eV, while the latter is a direct band gap semiconductor with a gap of 1.93 eV. Analysis of the optical absorption spectrum reveals that the g-Si3P3 sheet may have applications in solar absorbers owing to its narrow direct band gap and wide range optical absorption in the visible light spectrum.
![2-(1-azabicyclo[2.2.2]oct-3-yloxy)-1-cyclopentyl-1-phenylethanol hydrochloride (1:1)](http://img.cochemist.com/ccimg/152000/151937-76-7.png)
![2-(1-azabicyclo[2.2.2]oct-3-yloxy)-1-cyclopentyl-1-phenylethanol hydrochloride (1:1)](http://img.cochemist.com/ccimg/152000/151937-76-7_b.png)
![2-[(3-IODANYLPHENYL)METHYL]GUANIDINE](http://img.cochemist.com/ccimg/77700/77679-27-7.png)
![2-[(3-IODANYLPHENYL)METHYL]GUANIDINE](http://img.cochemist.com/ccimg/77700/77679-27-7_b.png)
![Benzene, 1-bromo-4-[(4-hexylphenyl)ethynyl]-](http://img.cochemist.com/ccimg/62900/62856-47-7.png)
![Benzene, 1-bromo-4-[(4-hexylphenyl)ethynyl]-](http://img.cochemist.com/ccimg/62900/62856-47-7_b.png)
![Technetium(1+)-99Tc,hexakis[1-(isocyano-kC)-2-methoxy-2-methylpropane]-, (OC-6-11)- (9CI)](http://img.cochemist.com/ccimg/109600/109581-73-9.png)
![Technetium(1+)-99Tc,hexakis[1-(isocyano-kC)-2-methoxy-2-methylpropane]-, (OC-6-11)- (9CI)](http://img.cochemist.com/ccimg/109600/109581-73-9_b.png)
