Co-reporter:Xukai Luo, Guangzhao Wang, Yuhong Huang, Biao Wang, Hongkuan Yuan, and Hong Chen
The Journal of Physical Chemistry C August 31, 2017 Volume 121(Issue 34) pp:18534-18534
Publication Date(Web):August 2, 2017
DOI:10.1021/acs.jpcc.7b03616
The graphene-like ZnO (g-ZnO) nanosheets were synthesized and shown to exhibit highly photocatalytic activity for the degradation of RhB under ultraviolet irradiation. In this work, we utilize cationic–anionic passivated codoping to explore the potential of the g-ZnO nanosheet for the design of efficient water redox photocatalysts by employing density functional theory calculations with the hybrid HSE06 functional. Our calculations show that anion–cation passivated codoped systems not only are more favorable than the corresponding monodoping in the g-ZnO nanosheet due to the Coulomb interactions but also effectively reduce the band gap without introducing unoccupied states which accelerate the electron–hole recombination. The charge-compensated P–Sc and C–Zr codoped g-ZnO nanosheets are energetically favorable for hydrogen evolution but not insufficient to produce oxygen, indicating that they could serve as Z-scheme photocatalysts. The C–Ti, N–Y, and P–Y codoped systems may be potential potocatalysts for photoelectrochemical water splitting to generate hydrogen due to their appropriate band gaps and band edge positions. In particular, the charge-compensated P–Y codoped g-ZnO nanosheet has the most excellent stability and the largest absorption region of visible light among these codoped systems. Further, we show that P–Y passivated codoping can reduce the overpotentials for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) of the g-ZnO nanosheet, indicating that the OER or HER on the P–Y codoped g-ZnO nanosheet can be easier driven by the irradiation-generated holes or electrons.
Journal of Materials Science 2017 Volume 52( Issue 9) pp:5333-5344
Publication Date(Web):07 February 2017
DOI:10.1007/s10853-017-0774-6
The charge-compensated N–F co-doping in combination with N or F mono-doping has been adopted to reduce the band-gap of KNbO\(_{3}\) so as to improve its photocatalytic efficiency under visible light for hydrogen generation by water splitting. The relative positions of N–F co-doping into O-sites of KNbO\(_{3}\) are considered to simulate the samples prepared by different experimental techniques. It is energetically unfavorable to form N mono-doped KNbO\(_{3}\) under any conditions, and the presence of F favors the N doping into KNbO\(_{3}\). Although N doping reduces the effective band-gap, the localized states above the Fermi level and the presence of charge-compensated oxygen defect will accelerate the electron-hole recombination and thus reduce photocatalytic efficiency, while F doping hardly affects the band-gap. The defect introduced by N doping has been completely passivated in the N–F co-doped system. All the N–F co-doped configurations considered here have suitable band-gaps to absorb visible light with respect to the water redox level. Even the N–F co-doped system with lower dopant concentration harvests obviously longer wavelength of visible light as compared to the pure system.
Physical Chemistry Chemical Physics 2017 vol. 19(Issue 41) pp:28216-28224
Publication Date(Web):2017/10/25
DOI:10.1039/C7CP04108J
In this work, we employ hybrid density functional theory calculations to design a two-dimensional layered CdS/C2N heterostructure for visible light photocatalytic water splitting to produce hydrogen. The calculation results show that the conduction band minimum (CBM) and the valence band maximum (VBM) of C2N monolayers are lower than those of CdS nanosheets by about 0.76 eV and 0.44 eV, respectively. The type-II band alignment, density of states, Bader charge analysis, and charge density difference of the CdS/C2N heterostructure indicate that the photogenerated electrons migrate from the CdS monolayer to the C2N monolayer, favoring the separation and transfer of photogenerated charge carriers, which restrains the recombination of photogenerated carriers and enhances the photocatalytic efficiency. The calculated band gap and optical absorption spectra reveal that the two-dimensional layered CdS/C2N heterostructure may be a potential photocatalyst for photo-electrochemical water splitting because of its appropriate band gap and excellent visible light absorption behavior. Moreover, the electronic and optical properties of the CdS/C2N heterostructure can be effectively modulated by the strain. These findings suggest that the C2N sheets are a promising candidate as metal-free co-catalysts for CdS photocatalysts, and also provide valuable information for experimentalists to design highly active and efficient visible light photocatalysts for water splitting.
The structural, electronic, and thermoelectric properties of DO3 V3Al in the paramagnetic (PM) and antiferromagnetic (AF) phases are investigated using the semi-classical Boltzmann theory in combination with deformation potential theory from first-principles calculations. The structural results are consistent with other theoretical and experimental data. AF-DO3 V3Al is verified to be a gapless semiconductor. Based on the calculated relaxation time τ and lattice thermal conductivity κL, the thermoelectric properties of PM-DO3 and AF-DO3 V3Al have been predicted. Compared with PM-DO3 V3Al, the AF-DO3 phase exhibits favorable thermoelectric performance. The optimized thermoelectric figure of merit ZT of the p-type AF-DO3 phase can be as high as 0.32 at T = 500 K. It is possible to make V3Al a promising candidate for efficient thermoelectricity by reducing its thermal conductivity.
In this theoretical study, the double-hole-mediated codoping strategy has been adopted to improve the photocatalytic activity of cubic KNbO3 as compared with the corresponding individual doping. The strong double-hole-mediated dopant–dopant coupling significantly reduces the effective bandgaps for the anionic–anionic (N–N, P–P, N–P, C–S) codoped systems with removing the appearing acceptor states above the Fermi level. No dopant–O coupling occurs in the cationic–anionic (V–C, Ti–P, Ti–N, Zr–P, Zr–N, Sc–S, Y–S) codoped systems. The V–C and Ti–P codoping could lead to narrowed bandgaps without unfilled localized states appearing above the Fermi level. N, Ti, Zr, Sc, Y monodoping and Ti–N, Zr–P, Zr–N, Sc–S, Y–S codoping introduce unoccupied impurity states between the valence band maximum and conduction band minimum, which makes them unfavorable for photocatalysis as these impurity states may serve as electron–hole recombination centers. For P–P, N–P, and C–S codoped systems, the intermediate states are higher or close to the hydrogen evolution potential, which is thermodynamically unfavorable for production of both oxygen and hydrogen. Producing hydrogen only, the N–N and C–S codoped KNbO3 materials will be good choices for Z-scheme photocatalysis. V, S, and V–C codoped KNbO3 may be promising visible light photocatalysts for water splitting, as they have suitable effective bandgaps without the introduction of unoccupied impurity states above the Fermi level, and they also own proper band edge positions with respect to the water redox level. The calculated optical absorption curves also indicate that C, V, and S monodoping and N–N, V–C, and Ti–P codoping can effectively enhance the visible light absorption.
Five-body Moshinsky brackets that relate harmonic oscillator wavefunctions in two different sets of Jacobi coordinates make it straightforward to calculate some matrix elements in the variational calculations of five-body systems. The analytical expression of these transformation coefficients and the computer code written in the Mathematica language are presented here for accurate calculations.Program summaryProgram title: FBMBCatalogue identifier: AEZT_v1_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEZT_v1_0.htmlProgram obtainable from: CPC Program Library, Queen’s University, Belfast, N. IrelandLicensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 15635No. of bytes in distributed program, including test data, etc.: 1498331Distribution format: tar.gzProgramming language: Mathematica.Computer: All computers running Mathematica.Operating system: Operating systems running Mathematica.RAM: 20265384 bytesClassification: 17.17.Nature of problem: The calculation of five-body Moshinsky bracketsSolution method: The method is based on the explicit expressions of five-body Moshinsky brackets presented in [1]Unusual features: The possibility of calculating five-body Moshinsky bracketsRunning time: Less than one second for a single five-body Moshinsky bracketReferences:[1] Shuyuan Xiao, Xueli Mu, Zhixuan Deng, Hong Chen, Journal of Mathematical Physics 56, 042102 (2015)
Co-reporter:Dr. Guang-Zhao Wang; Hong Chen;Gang Wu; An-Long Kuang; Hong-Kuang Yuan
ChemPhysChem 2016 Volume 17( Issue 4) pp:489-499
Publication Date(Web):
DOI:10.1002/cphc.201501037
Abstract
Monodoping with Mo, Cr, and N atoms, and codoping with Mo−N and Cr−N atom pairs, are utilized to adjust the band structure of NaNbO3, so that NaNbO3 can effectively make use of visible light for the photocatalytic decomposition of water into hydrogen and oxygen, as determined by using the hybrid density functional. Codoping is energetically favorable compared with the corresponding monodoping, due to strong Coulombic interactions between the dopants and other atoms, and the effective band gap and stability for codoped systems increase with decreasing dopant concentration and the distance between dopants. The molybdenum, chromium, and nitrogen monodoped systems, as well as chromium–nitrogen codoped systems, are unsuitable for the photocatalytic decomposition of water by using visible light, because defects introduced by monodoping or the presence of unoccupied states above the Fermi level, which promotes electron–hole recombination processes, suppress their photocatalytic performance. The Mo−N codoped NaNbO3 sample is a promising photocatalyst for the decomposition of water by using visible light because Mo−N codoping can reduce the band gap to a suitable value with respect to the water redox level without introducing unoccupied states.
Co-reporter:Yao Jiang, Hongkunag Yuan and Hong Chen
Physical Chemistry Chemical Physics 2015 vol. 17(Issue 1) pp:630-637
Publication Date(Web):05 Nov 2014
DOI:10.1039/C4CP03631J
To improve the photocatalytic activity of Cu2O for hydrogen production through water splitting, the band edges of Cu2O should be modified to meet the electronic transition of angular momentum selection rules (Δl = ±1) and match with the hydrogen or oxygen production levels. Upon analyzing the band structure of Cu2O and the chemical potentials of the dopants, we show that passivated codopants such as (Sn + B) can induce superior modification in the band edges of Cu2O: the conduction band edge is changed from the d band character of Cu atoms to the p band character of the Sn atom and shifted slightly downwards, while the valence band edge keeps the d band character of the Cu atoms and energy unchanged, indicating that the stringent requirements get satisfied. Moreover, the optical absorption spectrum of (Sn + B) codoped Cu2O shows a greatly improved absorption of visible light. The calculated defect formation energy shows that the codoping is energetically more favorable than mono-doping due to the Coulomb interactions and charge compensation effects.
Co-reporter:Guangzhao Wang, Hong Chen, Yang Li, Anlong Kuang, Hongkuan Yuan and Gang Wu
Physical Chemistry Chemical Physics 2015 vol. 17(Issue 43) pp:28743-28753
Publication Date(Web):22 Sep 2015
DOI:10.1039/C5CP04365D
To improve the photocatalytic performance of KNbO3 for the decomposition of water into hydrogen and oxygen, the electronic structure of KNbO3 should be modified to have a suitable bandgap with band edge positions straddling the water redox level so as to sufficiently absorb visible light. Hybrid density functional theory has been used to calculate the electronic structures of pure, N-, Mo-, and Cr-monodoped, and Mo–N and Cr–N codoped KNbO3. In particular, the influence of the relative positions of Mo–N or Cr–N codopants on the electronic structure of KNbO3 is discussed in detail to account for the possible difference in the photocatalytic activity of the codoped samples prepared by different experimental techniques. The defect formation energy calculations indicate that a N-doped system is difficult to form under any conditions and the codoped systems are energetically favorable under Nb-poor and O-rich conditions. It is interesting to find that the effective bandgap and stability for codoped systems decrease with the increase of the dopant concentration and/or the distance between dopants. Furthermore, the suitable bandgap and band edge position with respect to the water redox level make the Mo–N codoped systems good candidates for visible light photocatalytic decomposition of water to generate hydrogen.
Co-reporter:Yu Feng, Bo Wu, Hongkuan Yuan, Hong Chen
Journal of Alloys and Compounds 2015 Volume 623() pp:29-35
Publication Date(Web):25 February 2015
DOI:10.1016/j.jallcom.2014.09.129
•Interfacial MnSi atoms prefer to locate in the bridge sites between two Ag atoms.•A2 disorder of Co2MnSi layers near the interface is most likely to occur.•Spin polarization is reduced by interface itself and interfacial disorder.The performance of advanced current-perpendicular-to-plane giant magnetoresistance (MR) built of ferromagnetic (FM) electrodes and nonmagnetic metals as a spacer depends decisively on the properties of the FM/metal interface. Here we investigate the interface character between Co2MnSi and Ag by using the first-principles density functional simulations. To simulate the actual cases, we build two types of interfaces, namely tO and bO interfaces by connecting the most favorable MnSi-termination of nine ordered Co2MnSi layers to the top of Ag and the bridge site between two Ag atoms of seven atomic layers, respectively. Our calculations indicate that the bO interface is more probable to form in the growth than the tO interface due to the lower formation energy and interface free energy, and the interface states occur in the minority-spin gap, leading to the destruction of half-metallicity of the ordered Co2MnSi. Further, taking into account the atomic disorder of the Co2MnSi layers near the interface, we show that the A2 disorder is most likely to occur in the layers close to the interface due to the lower formation energy and interface free energy, and the interface states occurring in the spin-minority gap are strengthened and the spin polarization is further degraded by the A2 disorder of Co2MnSi layers. Therefore, the spin-polarization reduction induced by interface itself and the disorder of Co2MnSi layers close to the interface, together with the interface roughness indicated by the calculations, may be main causes of very low MR ratio.
International Journal of Hydrogen Energy 2014 Volume 39(Issue 8) pp:3780-3789
Publication Date(Web):6 March 2014
DOI:10.1016/j.ijhydene.2013.12.138
•Li can be decorated on the top of N in (AlN)n nanocages without clustering.•The fully decorated Lin(AlN)n nanocages can store hydrogen up to 7.7 wt%.•The binding energies of hydrogen to Li lie in the range of 0.1–0.2 eV/H2.The capability of Li-decorated (AlN)n (n = 12, 24, 36) nanocages for hydrogen storage has been studied by using density functional theory (DFT) with the generalized gradient approximation (GGA). It is found that each Al atom is capable of binding one H2 molecule up to a gravimetric density of hydrogen storage of 4.7 wt% with an average binding energy of 0.189, 0.154, and 0.144 eV/H2 in the pristine (AlN)n (n = 12, 24, 36) nanocages, respectively. Further, we find that Li atoms can be preferentially decorated on the top of N atoms in (AlN)n (n = 12, 24, 36) nanocages without clustering, and up to two H2 molecules can bind to each Li atom with an average binding energy of 0.145, 0.154, 0.102 eV/H2 in the Lin(AlN)n (n = 12, 24, 36) nanocages, respectively. Both the polarization of the H2 molecules and the hybridization of the Li-2p orbitals with the H-s orbitals contribute to the H2 adsorption on the Li atoms. Thus, the Li-decorated (AlN)n (n = 12, 24, 36) nanocages can store hydrogen up to 7.7 wt%, approaching the U.S. Department of Energy (DOE) target of 9 wt% by the year 2015, and the average binding energies of H2 molecules lying in the range of 0.1–0.2 eV/H2 are favorable for the reversible hydrogen adsorption/desorption at ambient conditions. It is also pointed out that when allowed to interact with each other, the agglomeration of Li-decorated (AlN)n nanocages would lower the hydrogen storage capacity.
Co-reporter:Yu Feng, Bo Wu, Hongkuan Yuan, Anlong Kuang, Hong Chen
Journal of Alloys and Compounds 2013 Volume 557() pp:202-208
Publication Date(Web):25 April 2013
DOI:10.1016/j.jallcom.2012.12.134
Using the first-principles calculations within density functional theory (DFT), we investigate the electronic and the magnetic properties of the bulk and the (1 0 0) surface of Hg2CuTi-type Heusler alloy Ti2CoAl. In the Ti2CoAl bulk, the calculated equilibrium lattice constant of 6.2 Å is detected. Due to different surroundings, the atomic magnetic moment (AMM) of Ti1 and that of Ti2 show distinct difference and the magnetic contribution of Ti1 is slightly larger than that of Ti2. In addition, our work indicate that the competition between RKKY mechanism and direct magnetic exchange among d-electron atoms plays a dominating role in determining the total magnetism. As for the Ti2CoAl (1 0 0) surface, we have studied five terminations and such studies reveal that the surface Ti1 and Co atoms prefer to move towards vacuum and the slab respectively while the surface Ti2 and Al atoms almost hold their positions unmoved in comparison with those in the bulk. Moreover, the analysis on surface magnetic behaviors show that owing to the surface effect, the AMM of surface Ti1 is enhanced obviously while that of Co atom is decreased in contrast with the bulk value and the AMM of Ti2 is very close to the bulk value. Further investigation on the PDOS indicate that because of surface states, the calculated five atom-terminations fail to preserve the half-metallicity which can be observed in the bulk. Different from the conventional Co-based Heusler alloy with Cu2MnAl-type structure, it is predicted with higher surface spin polarization in CoCo-termination than TiCo-, TiAl- and TiTi-termination, moreover the AlAl atomic surface also presents more superiority to other calculated surface systems.Highlights► Hg2CuTi-type Ti2CoAl is different from conventional Cu2MnAl-type structure. ► The atomic magnetic moments of Ti1 are different from that of Ti2 in bulk. ► The surface properties reveal that all terminations lose the half-metallicity. ► CoCo-, TiCo-, TiAl-, AlAl-termination are predicted with high spin polarization.
•Pd1−xCuxMnSb with three different spin alignments of Mn atoms is investigated.•As x = 0.75, an obvious ferromagnetic–antiferromagnetic phase transition appears.•Magnetic coupling mechanism of the phase transition is comprehensively discussed.•Electronic and magnetic properties in Pd1−xCuxMnSb are sensitive to spin alignment.By using the first-principles calculations within the density functional theory (DFT), we investigate the structure, magnetism and electronic properties of half-Heusler compound Pd1−xCuxMnSb with three different spin alignments of Mn atoms. For the ferromagnetic (FM) alloys, due to prominent RKKY-type magnetic coupling related to polarized sp-electrons, with increasing Cu-doped concentration x, total FM moments firstly enhance, then sharply drop off as x > 0.625. While in antiferromagnetic (AFM) states, owing to the strong AFM superexchange interactions mediated by nonmagnetic Cu atoms, Mn atomic magnetic moments (AMMs) monotonously decrease. As x = 0.75, an obvious FM-AFM phase transition is detected. Further analysis on electronic structure shows that the Fermi level gradually shifts towards high-energy orientation with the increase of Cu-doped concentration in both FM and AFM states, resulting consequently in an obvious variation of spin polarization ratio. By comparison of AFM1 and AFM2 alloys characterized by antiparallel Mn spin orientations each other with respect to (1 0 0) and (1 1 1) atomic planes respectively, within the range of x from 0.25 to 0.75, the smaller average bonding length causes stronger superexchange magnetic interaction, and leads to relatively lower Mn AMM and less electrons occupied at low-energy bands in AFM1 states, which implies that the electronic structure of the CuxPd1−xMnSb alloy is very sensitive to spin alignment.
The thermodynamic stability, magnetism and half-metallicity of Heusler alloy Co2MnX(X = Si, Ge, Sn)(1 0 0) surface are comprehensively investigated from the first-principles calculations. The calculated phase diagram indicates that with increasing core electrons of X atoms in Co2MnX(1 0 0) the CoCo termination will be faded out of the thermodynamic equilibrium region gradually. Due to the difference of CoX bonding the surface Co and Mn atoms prefer to move towards the slab and vacuum, respectively. By comparing with the bulk, the surface Co and Mn atomic magnetic moments (AMMs) are enhanced obviously because of the significant surface d-electronic localization. Further investigations of the partial density of states (PDOS) show that the half-metallicity observed in bulk has been destroyed by the surface states in deficient-Mn atomic terminated surface, only the terminations capped pure Mn atoms in Co2MnSi(1 0 0) and Co2MnGe(1 0 0) surfaces preserve spin-polarization of 100% instead of the Co2MnSn(1 0 0) surface, which is a possible explanation for low experimental tunnel magnetoresistance (TMR) value in Co2MnSn(1 0 0)-based magnetic tunnel junctions (TMJs).
The static electric polarizability and absorption spectrum of the coupled noble metal (Ag, Au, Cu) cluster-pair are investigated within density functional theory (DFT). The results show that the HOMO–LUMO gap gradually widens with increasing cluster distance D, and the static polarizability exhibits a maximal value as D is near the average bond length of cluster. In the absorption spectrum, the spectral strength is related to electric dipole moments which sensitively rely on D. With the increase of D the low-energy peaks (LEPs) obviously blue shift while the high-energy peaks (HEPs) keep their positions unmoved. The LEPs (HEPs) mostly comes from the transitions between near (far) the HOMO and LUMO energy levels. In these transitions, the low-energy excitations are dominantly contributed by d-electrons, indicating the fact that intense coupling effects can weaken the screen of d-electrons on sp-electrons. By means of the competition mechanism between charge transfer and electron cloud distortion, the spacing dependence behaviors of both electric and optical properties are explained self-consistently.Highlights► The electric and optical properties of a cluster-pair rely on cluster interval D. ► The maximal polarizability is presented as D is near the bond length of cluster. ► The low-energy (high-energy) peaks blue shift (keep unmoved) with increasing D. ► Intercluster coupling can weaken the screen of d-electrons on sp-electrons. ► The electronic behaviors are discussed for explaining calculated results properly.
Co-reporter:H. K. Yuan, H. Chen, A. L. Kuang, B. Wu, and J. Z. Wang
The Journal of Physical Chemistry A 2012 Volume 116(Issue 47) pp:11673-11684
Publication Date(Web):November 9, 2012
DOI:10.1021/jp307202t
The spin and orbital magnetic moments, as well as the magnetic anisotropy energy (MAE), of small 4d transition metal (TM) clusters are systematically studied by using the spin–orbit coupling (SOC) implementation of the density-functional theory (DFT). The effects of spin–orbit interactions on geometrical structures and spin moments are too weak to alternate relative stabilities of different low-lying isomers. Remarkable orbital contributions to cluster magnetic moments are identified in Ru, Rh, and Pd clusters, in contrast to immediate quenching of the atomic orbital moment at the dimer size in other elemental clusters. More interestingly, there is always collinearity between total spin and orbital moments (antiferromagnetic or ferromagnetic coupling depends on the constituent atoms whose 4d subshell is less or more than half-filled). The clusters preserve the validity of Hund’s rules for the sign of orbital moment. The calculations on MAEs reveal the complicated changes of the easy axes in different structures. The perturbation theory and the first-principles calculations are compared to emphasize how MAEs evolve with cluster size. Finally, large orbital moments combined with strong spin–orbit coupling are proposed to account for large MAEs in Ru, Rh, and Pd clusters.
Co-reporter:Tongyu Wang, Baihai Li, Jianhui Yang, Hong Chen and Liang Chen
Physical Chemistry Chemical Physics 2011 vol. 13(Issue 15) pp:7112-7120
Publication Date(Web):16 Mar 2011
DOI:10.1039/C0CP02007A
The formation of Pd/Au surfaces and their catalytic performance toward oxygen dissociation were investigated using periodic density functional methods. We show that Pd can readily incorporate into the second layer of Au(100) and Au(111) substrates with the assistance of Au vacancies. Pd/Au(100) exhibits better catalytic activity toward oxygen dissociation than Pd/Au(111). Specifically, the sub-layer Pd atoms of Pd/Au(100) can promote the oxygen dissociation and stabilize the surface structure after adsorbing oxygen atoms. On the contrary, the sub-layer Pd atoms of Pd/Au(111) slightly hinder the oxygen dissociation.
The first-principles calculations have been performed to understand the origin of magnetism in undoped GaN thin films. The results show that Ga vacancy, rather than that of N contributes the observed magnetism, and the magnetic moments mainly come from the unpaired 2p electrons at nearest-neighbor N atoms of the Ga vacancy. Calculations and discussions are also extended to bare and passivated GaN nanowires, We find that per Ga vacancy on the surface sites products the total magnetic moment of 1.0 while that inside of the nanowires can lead to the formation of a net moment of 3.0 . The coupling between two Ga vacancies is also studied and we found that the coupling is ferromagnetic coupling. The surface passivation with hydrogen is shown to strongly enhance the ferromagnetism. Our theoretical study not only demonstrates that GaN nanowire can be magnetic even without transition-metal doping, but also suggests that introducing Ga vacancy is a natural and an effective way to fabricate low-dimensional magnetic GaN nanostructures.
Detailed first-principles calculations have been performed on adsorption of closely spaced rows of Mn atoms on Si(1 0 0) (2×1). The optimized geometries and adsorption energies have been obtained. For adsorption of a single Mn atom on Si(1 0 0), binding at the subsurface site below the Si surface dimmer is the most stable adsorption site. For two Mn atoms adsorption models, we found that the h and i sites are the energetically most favorable structure. The magnetic moment of b site is 3.642 Bwhich is the largest in all possible surface-adatom configurations. We also found that the silicon surface is metallic for the coverages of 0.5 and 1 ML.
Co-reporter:Anlong Kuang, Hongkuan Yuan, Hong Chen
Journal of Molecular Structure: THEOCHEM 2009 Volume 910(1–3) pp:69-73
Publication Date(Web):30 September 2009
DOI:10.1016/j.theochem.2009.06.022
The first-principles calculations have been performed on the adsorption of tetrahedron- and rhombus-Nb4Nb4 clusters on the Si(001)-(4×2). The results show that both Nb4Nb4 configurations can be stably adsorbed on the Si(0 0 1) surface, and the adsorption of bidimensional Nb4Nb4 clusters is more stable than those of tetrahedron-Nb4Nb4. The energy barriers are very high which indicates that it is difficult for the Nb4Nb4 clusters to diffuse. The work functions of the most stable adsorption sites decrease compared with that of the clean Si(0 0 1) surface, which demonstrates that the electronic charges transfer from the Nb4Nb4 clusters to the Si(0 0 1) surface.
Co-reporter:Ting Zhou, Yu Feng, Xiaorui Chen, Hongkuan Yuan, Hong Chen
Journal of Magnetism and Magnetic Materials (1 February 2017) Volume 423() pp:306-313
Publication Date(Web):1 February 2017
DOI:10.1016/j.jmmm.2016.09.112
Highlights•Charge compensated codoping for Ti2NiAl inverse Heusler alloy.•The Co+Si codoping is more favorable than the Co/Si monodoping.•The codoped such as Ti2Ni0.5Co0.5Al0.5Si0.5 process robust half-metallicity.Half-metallicity and magnetism of Ti2Ni1−x CoxAl1−y Siy, which are obtained by Co/Si substitutions for Ni/Al of inverse Heusler alloy Ti2NiAl, are investigated by first-principle calculations based on density functional theory (DFT). The optimized lattice constants of the doped systems all conform to the Vegard law as the increase of the impurity concentration, and the magnetic moments obey the Slater-Pauling rule when the half-metallicity is retained. The defect formation energies of the codoped systems are lower than those of the monodoped systems due to the charge compensation effects, thus the Co+Si codoping is more favorable in energy than the Co/Si monodoping. Furthermore, for the Co and Si monodoped systems, the Co monodoping retains the minority-spin bandgap unchanged although the Fermi level moves towards high energy region, and the Si monodoping leads to the minority-spin bandgap narrowing and even the loss of half-metallicity at the high concentration, while for the Co+Si codoped systems, the majority of the codoped compounds obviously show more stable half-metallicity and the minority-spin gap get widened. In particular, the minority-spin band gap of the codoped compounds Ti2Ni0.5Co0.5Al0.5Si0.5, Ti2Ni0.25Co0.75Al0.5Si0.5, and Ti2NiCo Al0.25Si0.75 are widened distinctly and their Fermi level are adjusted to the middle of the minority-spin gap, indicating that they possess robust half-metallicity and thus they are promising candidates for spintronics applications.
Co-reporter:Yao Jiang, Hongkunag Yuan and Hong Chen
Physical Chemistry Chemical Physics 2015 - vol. 17(Issue 1) pp:NaN637-637
Publication Date(Web):2014/11/05
DOI:10.1039/C4CP03631J
To improve the photocatalytic activity of Cu2O for hydrogen production through water splitting, the band edges of Cu2O should be modified to meet the electronic transition of angular momentum selection rules (Δl = ±1) and match with the hydrogen or oxygen production levels. Upon analyzing the band structure of Cu2O and the chemical potentials of the dopants, we show that passivated codopants such as (Sn + B) can induce superior modification in the band edges of Cu2O: the conduction band edge is changed from the d band character of Cu atoms to the p band character of the Sn atom and shifted slightly downwards, while the valence band edge keeps the d band character of the Cu atoms and energy unchanged, indicating that the stringent requirements get satisfied. Moreover, the optical absorption spectrum of (Sn + B) codoped Cu2O shows a greatly improved absorption of visible light. The calculated defect formation energy shows that the codoping is energetically more favorable than mono-doping due to the Coulomb interactions and charge compensation effects.
Co-reporter:Tongyu Wang, Baihai Li, Jianhui Yang, Hong Chen and Liang Chen
Physical Chemistry Chemical Physics 2011 - vol. 13(Issue 15) pp:NaN7120-7120
Publication Date(Web):2011/03/16
DOI:10.1039/C0CP02007A
The formation of Pd/Au surfaces and their catalytic performance toward oxygen dissociation were investigated using periodic density functional methods. We show that Pd can readily incorporate into the second layer of Au(100) and Au(111) substrates with the assistance of Au vacancies. Pd/Au(100) exhibits better catalytic activity toward oxygen dissociation than Pd/Au(111). Specifically, the sub-layer Pd atoms of Pd/Au(100) can promote the oxygen dissociation and stabilize the surface structure after adsorbing oxygen atoms. On the contrary, the sub-layer Pd atoms of Pd/Au(111) slightly hinder the oxygen dissociation.
Co-reporter:Guangzhao Wang, Hong Chen, Yang Li, Anlong Kuang, Hongkuan Yuan and Gang Wu
Physical Chemistry Chemical Physics 2015 - vol. 17(Issue 43) pp:NaN28753-28753
Publication Date(Web):2015/09/22
DOI:10.1039/C5CP04365D
To improve the photocatalytic performance of KNbO3 for the decomposition of water into hydrogen and oxygen, the electronic structure of KNbO3 should be modified to have a suitable bandgap with band edge positions straddling the water redox level so as to sufficiently absorb visible light. Hybrid density functional theory has been used to calculate the electronic structures of pure, N-, Mo-, and Cr-monodoped, and Mo–N and Cr–N codoped KNbO3. In particular, the influence of the relative positions of Mo–N or Cr–N codopants on the electronic structure of KNbO3 is discussed in detail to account for the possible difference in the photocatalytic activity of the codoped samples prepared by different experimental techniques. The defect formation energy calculations indicate that a N-doped system is difficult to form under any conditions and the codoped systems are energetically favorable under Nb-poor and O-rich conditions. It is interesting to find that the effective bandgap and stability for codoped systems decrease with the increase of the dopant concentration and/or the distance between dopants. Furthermore, the suitable bandgap and band edge position with respect to the water redox level make the Mo–N codoped systems good candidates for visible light photocatalytic decomposition of water to generate hydrogen.
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