•We investigate of H2 adsorption on Fe, Co, Ni-decorated B38 fullerene based on DFT.•Fe, Co, Ni atoms can stably on the surface of B38 without clustering.•Each Fe, Co, Ni atom can store 6H2 molecules with moderate average adsorption energy.The hydrogen storage capacity of M-decorated (M = Fe, Co, Ni) B38 fullerene is investigated using first-principles calculations based on density functional theory. The Fe, Co, Ni atoms are strongly bound on hexagonal holes of B38 fullerene without clustering. Fe4B38 (Co4B38 and Ni4B38) adsorbs 24H2 with moderate average adsorption energy of 0.175 (0.184 and 0.202) eV/H2. Based on density functional theory, the gravimetric density of Fe4B38 (Co4B38 and Ni4B38) could potentially reach 7.34 (7.21 and 7.22) wt%, respectively. Therefore, we infer that M-decorated (M = Fe, Co, Ni) B38 fullerene could be a candidate for further investigation as an alternative material for hydrogen storage.Download high-res image (118KB)Download full-size image

•The vDW, LDA and PBE functionals are used for studying H2 storage property.•Li atoms can disperse distribution on the borophene surface.•Li decorated borophene has high hydrogen storage capacities.In this work, we calculate stabilities, electronic properties and hydrogen adsorption properties of Li-decorated freestanding borophene. It was studied through three functionals (vDW, LDA and PBE) of the first principles density functional theory (DFT) methods. It was found that the adsorption energy of H2 on the pure borophene was small. The Li atoms decoration can improve the H2 adsorption capacity. By virtue of the larger binding energy than that for bulk Li, Li atoms can be adsorbed steadily and not form the clusters on the 2 × 2 borophene supercell surface. For single Li atom adsorbed, the maximum number of uptake is three hydrogen molecules. But for Li adsorbed on both sides of borophene, each Li atom can absorb up to four H2 molecules. Its hydrogen storage capacity reaches up to 13.7 wt% with an average adsorption energy of 0.142 and 0.176 eV/H2 for vDW and LDA functional without the consideration of temperature, respectively. At the room temperature, the hydrogen capacity is up to 9.1 wt%. This study suggests that Li-decorated borophene is a potential hydrogen storage medium.Download high-res image (221KB)Download full-size image

Using time-dependent density function theory (TDDFT), we have carried out a systematic study of collective excitations of the AB-stacked and AA-stacked few-layer graphene nanostructures with rectangle geometries. We found little effect of stacking sequence on the excitation properties of few-layer graphene nanostructures when the polarized direction of impulse excitation is in the armchair-edge or in the zigzag-edge directions. However, the effect of the stacking sequence becomes significant when the polarized direction was perpendicular to the layers. The absorption strength in the bilayer/trilayer system is slightly more than twice/three times as strong as that in the monolayer system. With the increase of the number of the layers, in the lower-energy resonance zone, absorption spectra are blue-shifted. The increasing strength of the optical absorption has also been found when the interlayer distance is increased followed by red shift in the supreme absorption peak. We found high energy resonances of πplasmons at 4–8 eV are localized in the boundary region showing dipole-like character. The current findings may pave a way for the potential applications in UV regions if there are available nanomechanical devices to tune stacking and interlayer distance.

•Coarse-grained molecular dynamics is used to study the mechanical properties of multi-layer graphene.•The mechanical properties of multi-layer graphene tend to be less sensitive to temperature as the layer increases.•Our study shows the mutilayer-graphene with SW defects distributed regularly is more stable than the system with defects distributed randomly.•Graphene with different coverage of defects has been studied.In this work, we investigate the effect of temperature, defect, and strain rate on the mechanical properties of multi-layer graphene using coarse-grained molecular dynamics (CGMD) simulations. The simulation results reveal that the mechanical properties of multi-layer graphene tend to be less sensitive to temperature as the layer increases, but they are sensitive to the distribution and coverage of Stone-Wales (SW) defects. For the same number of defect, there is less decline in the fracture stress and Young's modulus of graphene when the defects have a regular distribution, in contrast to random distribution. In addition, Young's modulus is less influenced by temperature and defect, compared to fracture stress. Both the fracture stress and Young's modulus have little dependence on strain rate.

•MRCI/aV5Z approach including valence and Rydberg states was used to investigate the PECs and TDMCs.•The active spaces have not effect on PECs, but it had a significant influence on TDMCs.•The line intensities were presented of γ and β systems for 296 K temperature including seven bands.Highly correlated ab initio calculations were performed in order to obtain an accurate determination of the γ(A2Σ+-X2П) system and β(B2П-X2П) system of the NO molecule. The multi-reference configuration interaction (MRCI) approach was used to investigate the potential energy curves and transition dipole moment curves of the γ and β systems. The potential energy curves of the three states agreed well with Rydberg-Klein-Rees (RKR) potential using aug-cc-pV5Z basis set. The active space had a significant influence on transition dipole moment curves, but it hardly effected on potential energy curves. We find that using a (4s/4πx/4πy/0δ) active space produces results significantly closer to experiment than a (4s/3πx/3πy/0δ) active space. We correctly and fully described their diffuse wave functions by the obvious balance between valence and Rydberg character of X2П, A2Σ+, and B2П states. Moreover, the Einstein A coefficient were calculated to predict the absolute intensities. The line lists were presented the intensities of γ system and β system from 296 K to 6000 K which included 0-0, 0-1, 0-2, 0-3, 1-0, 1-1, 1-2, and 2-0 bands.Download high-res image (93KB)Download full-size image

•We investigate of H2 adsorption on Ti-decorated B38 fullerene based on DFT.•Ti atoms can stably on the surface of B38 without clustering.•Each Ti atom can store six hydrogen molecules with the moderate average adsorption energy.In the present study we investigate the stabilities, electronic properties and the hydrogen storage capacity of Ti-decorated B38 fullerene. All calculations have been performed by using first-principles calculations based on density functional theory. Our results show Ti atoms can be attached on top of the center of hexagonal holes of B38 fullerene with large binding energy (5.67 eV). Each Ti atom can bind up to six hydrogen molecules with an average adsorption energy of 0.22 eV/H2. While the B38 fullerene coated with 4 Ti atoms (4Ti/B38) can store 24 H2 molecules, the gravimetric density reaches up to 7.44 wt% with an average adsorption energy of 0.23 eV/H2. Based on these results we infer that Ti-decorated B38 fullerene is a potential material for hydrogen storage with high capacity and might motivate active experimental efforts in designing hydrogen storage media.

•The stabilities of Li decorated BN analogs of γ-graphyne are investigated.•van der Waals interactions are corrected for H2 adsorption.•Both of 2Li/BN-yne and 2Li/BNC-yne are potential materials for hydrogen storage.Li-decorated BN analogs of γ-graphyne have a potential for high density hydrogen storage. We investigate the structural stabilities of Li decorated double-sided BN analogs of γ-graphyne (2Li/BN-yne and 2Li/BNC-yne) and the hydrogen storage capacities based on density-functional theory (DFT) including van der Waals interactions. The two materials both are able to absorb six hydrogen molecules with a maximum hydrogen gravimetric density of 6.865 and 8.797 wt%, respectively. And the average binding energies are 0.335 and 0.342 eV/H2 using the vdW-DF2 functional, respectively. The hydrogen binding mechanisms are investigated by analyzing the partial density of state (PDOS) and charge transfer of the complexes.

In this study, first-principles time-dependent density functional theory calculations were used to demonstrate the possibility to modulate the amplitude of the optical electric field (E-field) near a semiconducting graphene nanoribbon. A significant enhancement of the optical E-field was observed 3.34 Å above the graphene nanoribbon sheet, with an amplitude modulation of approximately 100 fs, which corresponds to a frequency of 10 THz. In general, a six-fold E-field enhancement could be obtained, which means that the power of the obtained THz is about 36 times that of incident UV light. We suggest the use of semiconducting graphene nanoribbons for converting visible and UV light into a THz signal.

Noble metal nanoparticles can modify the optical properties of graphene. Here we present a detailed theoretical analysis of the coherent resonance of quantum plasmons in the graphene–gold cluster hybrid system by using time dependent density functional theory (TDDFT). This plasmon coherent effect is mainly attributed to the electromagnetic field coupling between the graphene and the gold cluster. As a result, the optical response of the hybrid system exhibits a remarkably strong, selectable tuning and polarization dependent plasmon resonance enhanced in wide frequency regions. This investigation provides an improved understanding of the plasmon enhancement effect in a graphene-based photoelectric device.

•There was an increase for the activity of the DG by introducing B-dopant.•The adsorption of H2 on Pd/DVG leaded to dissociated and chemisorbed state.•The activated states of H2 occurred on SVG with stretched H–H bonds.The effect of a combination of B-doping and vacancy-defect on the atomic adsorption of hydrogen on Pd-decorated graphene have been investigated using density functional theory simulations. The introducing of defect and B-dopant enhanced the adsorption of hydrogen molecule and the PDOS results indicated that the enhancement was contributed by the hybridization of B and H atoms. Furthermore, the adsorption of hydrogen molecule on Pd-decorated double-vacancy (DV) defective graphene lead to dissociated and chemisorbed states with the two separated H atoms bonding to the C atoms at vacancy sites. Interestingly, the B-doping decreased the interaction between the Pd-adatom and the defected graphene but increased the stability of the adsorption of dissociated H2. The activated states of H2 molecule occurred in the adsorption on single-vacancy (SV) defected graphene with stretched H–H bonds. Our results provide a potential approach for the engineering of graphene for hydrogen storage applications.The adsorption of hydrogen on Pd-decorated modified graphene, considering various adsorption structures, were studied by performing the atomic structures, geometry parameters, and electronic properties to explore the effect of a combination of B-dopant and defect on the H2 adsorption.

•The electronic and optical properties of oxygen-defected structures are investigated.•The absorption peaks of defected structures are much stronger in VIS to UV.•The energy loss function below 2 eV is caused by oxygen-excess defected structures.The oxygen-excess structures include oxygen dangling bond, peroxy linkage (POL), peroxy radical (POR) and interstitial oxygen molecule or ozone molecule defects, while the oxygen-deficient structures include neutral oxygen vacancy, E′ center and oxygen double-bond. For both the undefected and the various defected structures, the electronic and optical properties are calculated by plane-wave pseudo potential density functional theory. The oxygen-deficient defected structures lead to the remarkable increases in the density of states (DOS) at the top of valence band and near the bottom of the conduction band. The oxygen-excess defected structures change the distribution of defect levels and there appear new levels between the valence band and conduction band. All the defects lead to the increase of static dielectric constants and the enhancing absorption in the low energy range. Absorption peaks can be observed below 2 eV for NBOHC defected structures. Though the energy loss is generated at the lower energy region, the loss strength below 2 eV for oxygen-excess defected structures is stronger than oxygen-deficient defected structures. During the calculation the dangling bond in the structures are neutralized by hydrogen atoms. This work may give insights into the laser induced damage towards to vitreous silica.

Porous potassium-promoted iron oxide, with the potassium content of 8 wt% can produce dense hydrogen materials as a catalyst. In this letter, we use density functional theory (DFT) and the generalized gradient approximation (GGA) to study this catalyst. Rhombohedral α-Fe2O3 is used to build a porous model. We randomly put potassium atoms in the clean porous structure and iron-vacant defective structure. The results show that potassium atoms eventually exist in the form of clusters in the two samples. To further study the effect of potassium, clean and two K-promoted models are filled with the same quantity of H2. We obtain that the existence of potassium clusters prevents hydrogen molecules to dissociate into atoms in non-defective porous iron oxide. Most of the hydrogen atoms still exist in the form of hydrogen molecules in three models. The structures of potassium clusters for 2 ≤ N ≤ 8 in the porous model are also discussed, in contrast to the isolated clusters.

Four types of tetraphenyl silsesquioxane based covalent-organic frameworks (sil-COFs) were designed with the ctn and bor net topologies using molecular mechanics. The computed results revealed that these sil-COFs possess excellent structural properties, such as high porosity (89–95%) and large H2 accessible surface area (5476–6331 m2 g−1), which is advantageous to hydrogen storage. The H2 adsorption isotherms of these sil-COFs were simulated using the grand canonical Monte Carlo (GCMC) method at 77 K and 298 K. The simulated results indicated that at 77 K, sil-COF-4 has the highest gravimetric hydrogen storage capacity of 36.82 wt%, while sil-COF-1 has the highest volumetric hydrogen storage capacity of 63.53 g L−1. At 298 K, sil-COF-4 has the highest gravimetric hydrogen uptake of 5.50 wt%, which already exceeds the U.S. Department of Energy's goal (4.5 wt%) for 2017 and is also very close to the criterion of 6 wt% for practical applications of hydrogen at room temperature. In addition, two possible schemes are proposed to synthesize the sil-COFs.

•The presence of Stone–Wales defect in graphene enhanced the adsorption of H2CO molecule.•There was chemical bond forming between H2CO molecule and TM atoms (Cr, Mn and Co) doped defected graphene.•The adsorption of H2CO molecule changed the conductance and magnetic properties of Cr and Mn doped defected graphene.Adsorption of H2CO molecule on Cr, Mn and Co doped Stone–Wales defected graphene were theoretically studied using density functional theory (DFT) method. It was found that H2CO molecule had no considerable interaction with perfect or SW-defected graphene, but the presence of Stone–Wales defect in graphene enhanced the adsorption of H2CO, which exhibited larger binding energy and smaller bond distance. Chemisorptions were observed on the transition metal (TM) atoms (Cr, Mn and Co) doped structures. Compared with TM-doped perfect graphene, the binding energy of H2CO molecule on TM-doped defective graphene can be enlarged by the introduction of SW-defect. The density of states (DOS) showed that the contribution of hybridization between O atom of H2CO molecule and transition metal atom is mainly from the p or d orbitals. Furthermore, adsorption of H2CO affected the electronic conductance of the Cr and Mn doped defective graphene, which can be seen signal of gas sensor. It is expected that the results could provide useful information for the design of H2CO sensing devices.

•The electronic and magnetic properties of TM atoms absorbed on SW-defect graphene are investigated.•The absence of SW defect induce an opening of band gap of graphene.•The C atoms around the SW defect are more active to absorb the TM atoms.The adsorption of transition metal (TM) atoms on graphene monolayer with Stone–Wales (SW) defects was investigated using the first-principles density functional theory (DFT). The binding energy, geometry, charge transfer, band structure, density of states, and magnetic properties were calculated and analyzed. It was found that the presence of SW defect enhanced the interaction between TM adatoms and graphene and had a strong impact on the corresponding band structure. The partial density of states (PDOS) analysis suggested a strong hybridization of TM-3d orbital and C-2p orbital. These results indicated that the properties of graphene could be strongly modified by introducing Stone–Wales defect and adsorbed 3d transition-metal adatoms.

The plasmonic properties of gold nanotube assemblies are investigated using time-dependent density functional theory (TDDFT). The plasmon resonance peak of gold nanotube assemblies is strongly dependent on the polarization direction and gap distance. The optical absorption exhibits that the resonances correspond to different modes. These modes can be regarded as dipole interaction from their charge distribution. The interaction between nanotubes is opposite for different polarization direction, which causes distinct anisotropy effects in the spectral behavior. These results offer us alternative ways to tune the plasmon resonance in this structure.

A novel type of three-dimensional (3D) tetrahedral silsesquioxane-based porous frameworks (TSFs) with diamond-like structure was computationally designed using the density functional theory (DFT) and classical molecular mechanics (MM) calculations. The hydrogen adsorption and diffusion properties of these TSFs were evaluated by the methods of grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations. The results reveal that all designed materials possess extremely high porosity (87–93 %) and large H2 accessible surface areas (5,268–6,544 m2 g−1). Impressively, the GCMC simulation results demonstrate that at 77 K and 100 bar, TSF-2 has the highest gravimetric H2 capacity of 29.80 wt%, while TSF-1 has the highest volumetric H2 uptake of 65.32 g L−1. At the same time, the gravimetric H2 uptake of TSF-2 can reach up to 4.28 wt% at the room temperature. The extraordinary performances of these TSF materials in hydrogen storage made them enter the rank of the top hydrogen storage materials so far.

In this paper, we performed a multiscale study on the hydrogen storage capacity of Li–Sc doped and Li-C60 injected covalent organic frameworks (COFs)-based phthalocyanine, porphyrin and TBPS COFs. We combined the first-principles studies of hydrogen adsorption and grand canonical Monte Carlo (GCMC) simulations of hydrogen adsorption in nine designed COFs. The first-principles calculations revealed that the Li atoms can be doped on the surface of the Sc-doped COFs with binding energy from −83.9 to −160.2 kJ/mol. Each Li atom can bind three H2 molecules with the adsorption energy between −16.8 and −20.0 kJ/mol. The GCMC simulations have predicted that all the nine designed COFs can reach the Department of Energy’s 2015 target (5.5 wt% and 40 g/L) at T = 77 K and P = 100 bar. The optimum conditions of hydrogen storage for Li-C60@Li–Sc-PR-TBPS2, the promising materials, are T = 193 K (−80 °C) and P = 100 bar with a gravimetric H2 density of 8.19 wt% and volumetric H2 uptake of 42.6 g/L. Finally, we further convinced the importance of Sc in improving H2 uptake in doped COFs.

•The existence of vacancy in graphene enhanced the adsorption of H2CO molecule.•There was chemical bond forming between H2CO molecule and dopants (B, N, and S) in modified graphene.•The adsorption of H2CO molecule changed the conductivity of B and S doped defected graphene.The adsorption of formaldehyde (H2CO) on modified graphene sheets, combining vacancy and dopants (B, N, and S), was investigated by employing the density functional theory (DFT). It was found that the vacancy-defected graphene was more sensitive to absorb H2CO molecule compared with the pristine one. Furthermore, the H2CO molecule tended to be chemisorbed on vacancy-defected graphene with dopants, which exhibited larger adsorption energy and net charge transfer than that of one without dopants. The results of partial electronic density of states (PDOS) indicated that the defect-dopant combination effect on the adsorption process was mainly owing to the contribution of the hybridization between dopants and C atoms around the vacancy. We hope our results will be useful for the application of graphene for chemical sensors to detect formaldehyde gas.

Applying density functional theory (DFT) calculations, we have designed fullerenes (C20, C24, C26, C28, C30, C36, C60 and C70) intercalated phthalocyanine covalent organic frameworks (Cn-Pc-PBBA COFs). First principles molecular dynamics (MD) simulations showed that the structures of Cn-Pc-PBBA COFs are stable at room temperature and even at higher temperature (500 K). The interlayer distance of Pc-PBBA COF has been expanded to 7.48–13.25 Å by the intercalated fullerenes, and the pore volume and surface area were enlarged by 2.3–3.1 and 2.0–2.6 times, respectively. The grand canonical Monte Carlo (GCMC) simulations show that our designed Cn-Pc-PBBA COFs exhibit a superior hydrogen storage capability: at 77 K and P = 100 bar, the hydrogen gravimetric and volumetric uptakes reach 9.4–12 wt% and 48.1–52.2 g L−1, respectively. To meet the requirement for practical application in hydrogen storage, we use the Li-doping method to modify the hydrogen storage performance of Cn-Pc-PBBA COFs. Our results show that the Li atoms can stably locate on the surface of C30-, C36, C60 and C70-Pc-PBBA COFs. At T = 298 K and P = 100 bar, for these four Li-doped Cn-Pc-PBBA COFs, the gravimetric and volumetric uptakes of H2 reach 4.2 wt% and 18.2 g L−1, respectively.

The hydrogen spillover mechanism, including the H chemisorption, diffusion, and H2 associative desorption on the surface of COFs and H atoms migration from metal catalyst to COFs, have been studied via density functional theory (DFT) calculation. The results described herein show that each sp2 C atom on COFs' surface can adsorb one H atom with the bond length dC–H between 1.11 and 1.14 Å, and the up-down arrangement of the adsorbed H atoms is the most stable configuration. By counting the chemisorption binding sites for these COFs, we can predict the saturation storage densities. High hydrogen storage densities show that the gravimetric uptakes of COFs are in the range of 5.13–6.06 wt%. The CI-NEB calculations reveal that one H atom diffusing along the C–C path on HHTP surface should overcome the 1.41–2.16 eV energy barrier. We chose tetrahedral Pt4 cluster and HHTP as the representative catalyst and substrate, respectively, to study the H migration from metal cluster to COFs. At most, two H atoms can migrate from Pt4 cluster to HHTP substrate. The migration reaction is an endothermic process, undergoing an activation barrier of 1.87 eV and 0.57 eV for the first and second H migration process, respectively. Three types of H2 associative desorption from hydrogenated COFs were studied: (I) the two H adatoms recombining to one H2 molecule with a recombination barrier of 4.28 eV, (II) the abstraction of adsorbed H atoms by gas-phase hydrogen atoms through ER type recombination reactions with a recombination barrier of 1.05 eV, (III) the H2 desorption through the reverse spillover mechanism with an energy barrier of 2.90 eV.

Light metal borohydrides and especially lithium borohydride (LiBH4) has attracted a great deal of attention in recent years because of its large gravimetric and volumetric hydrogen density. However, LiBH4 is thermodynamically too stable for the hydrogenation/dehydrogenation cycles to proceed at practical pressure and temperature. In this work, we offer a new route to use LiBH4 as hydrogen storage material that various nanopores within LiBH4 crystal are constructed for physisorbing molecular hydrogen. The interaction between a single H2 molecule and the nanoporous LiBH4 is proposed by density functional theory (DFT). Calculating adsorption isotherms and isosteric heats of adsorption of H2 in designing new sorbents using grand canonical Monte Carlo (GCMC) simulations are performed at 298 and 77 K, in a broad range of 0.1–100 bar. It is identified that the porosity of the material considered has a strong impact on the adsorption capacity. At room temperature, values of hydrogen adsorption capacities of a maximum of 1.35 wt.% in gravimetric, 4.70 g/L of volumetric have been obtained at 100 bar, respectively. At 77 K, the absolute hydrogen storage capacity in the best structure considered is 9.36 wt.% and 35.41 g/L at 100 bar as well as the excess hydrogen storage of 5.87 wt.% and 21.39 g/L at 40 bar, respectively. These results may be used to provide a new route for using LiBH4 as a hydrogen storage medium.Highlights► Various nanopores within LiBH4 crystal are constructed for physisorbing molecular hydrogen. ► The adsorption energies of hydrogen molecule in the pores are 0.050–0.299 eV. ► The porosity of the material considered has a strong impact on the adsorption capacity. ► The absolute hydrogen storage capacity in the ideal structure is 9.36 wt.% and 35.41 g/L at 77 K.

A new class of 3D adamantane-based aromatic framework (AAF) with diamond-like structure was computationally designed with the aid of density functional theory (DFT) calculation and molecular mechanics (MM) methods. The hydrogen storage capacities of these AAFs were studied by the method of grand canonical Monte Carlo (GCMC) simulations. The calculated pore sizes of three AAFs reveal that AAF-1 and AAF-2 belong to microporous materials, while AAF-3 is a member of mesoporous materials. The GCMC results reveal that at 77 K and 100 bar, AAF-3 exhibits the highest gravimetric hydrogen uptake of 29.50 wt%, while AAF-1 shows the highest volumetric hydrogen uptake of 63.04 g L−1. In particular, the gravimetric hydrogen uptake of AAF-3 reaches the Department of Energy's target of 6 wt% at room temperature. The extraordinary performances of these new AAFs in hydrogen storage have made them enter the list of top hydrogen storage materials up to now.

Which is the first step in the decomposition process of nitromethane is a controversial issue, proton dissociation or C–N bond scission. We applied reactive force field (ReaxFF) molecular dynamics to probe the initial decomposition mechanisms of nitromethane. By comparing the impact on (010) surfaces and without impact (only heating) for nitromethane simulations, we found that proton dissociation is the first step of the pyrolysis of nitromethane, and the C–N bond decomposes in the same time scale as in impact simulations, but in the nonimpact simulation, C–N bond dissociation takes place at a later time. At the end of these simulations, a large number of clusters are formed. By analyzing the trajectories, we discussed the role of the hydrogen bond in the initial process of nitromethane decompositions, the intermediates observed in the early time of the simulations, and the formation of clusters that consisted of C–N–C–N chain/ring structures.

Using first-principles calculations, we investigate the adsorption behaviors of H2 in B/C/N sheets (including BCN, BC2N, and BC3N) and discuss the effect of external electric fields on H2 adsorbed for BCN and BC2N sheets. For a single H2 adsorbed on BCN and BC2N sheets, the adsorption energy increases dramatically with the electric field intensity increasing, and the maximum adsorption energy can reach 0.55 eV in the electric field of F = 0.050 a.u. and one layer H2 can adsorb on BCN and BC2N sheets, corresponding to the maximum hydrogen storage capacity of 5.1 wt%. The average adsorption energy calculated larger than that of in the field-free case.

The binding property of hydrogen on organometallic compounds consisting of Co, and Ni transition metal atoms bound to CmHm rings (m = 4, 5) is studied through density functional theory calculation. CoCmHm and NiCmHm complexes can store up to 3.49 wt% hydrogen with an average binding energy of about 1.3 eV. The adsorption characteristics of hydrogen to organometallic compounds are investigated by analyzing vibrational spectra of CoC4H4(H2)n and NiC4H4(H2)n (n = 0, 1, 2). The kinetic stability of these hydrogen-covered organometallic complexes is assured by analyzing the energy gap between the highest occupied molecular orbitals and the lowest unoccupied molecular orbitals. It is also discussed the application of 18-electron rule in predicting maximum number of hydrogen molecules that could be adsorbed by these organometallic compounds.

The electronic and band structure for (14, 0) single wall carbon nanotube (SWCNT) with the HCl molecule and H2 molecule inside are investigated by using a first-principles method with the pseudopotential density functional theory (DFT). The calculated density of states and band structures can elucidate the differences for the behavior of HCl and H2 inside SWCNT. The HCl molecule has a binding energy about −0.24 eV when it is put inside a (14, 0) SWCNT. Compared to HCl molecule, H2 did not induce any obvious change in the band structure and electronic property. A direct band gap 0.71 eV is obtained with HCl molecule inside (14, 0) CNT, which is larger than the value for pure CNT and with H2 molecule inside (14, 0) SWCNT.

DFT/B3LYP calculations were carried out on several π-complexes formed by cations and anions with annelated benzene, respectively. The binding energies obtained with standard method were corrected by basis set superposition error (BSSE) and zero-point energy (ZPE) during the geometry optimization for all complexes at the same levels of theory, respectively. Some different aspects of the π–cation have been compared to those of π–anion, involving in binding energy changes in effect of ring annelation, the aromaticity of the ring upon complexation, Mulliken and NBO charge-transfer. The effect of BSSE correction during the optimization is very important in some π–anion complexes whether or not using diffuse functions in basis set, and results with at least one set of diffuse functions 6-31+G(d) basis set is a little better than results obtained by 6-31G(d, p) basis set for some π–anion especially for F− complexes.

We study the density of state (DOS), band structure (BS), and atomic orbit projected density of state (PDOS) of paracetamol crystal adopting the density functional theory (DFT) technique in the local density approximation (LDA). The band structure around the Fermi level and the contributions from p-type orbit of C, N, O, and s-type orbit of H to the total density of state (TDOS) are addressed, and we find that the electronic characteristic is the key to form the hydrogen bond between O and H atoms. We show that the structure of paracetamol crystal consists of the –OH···O=C and –NH···OH hydrogen-bonding cycle by studying a single paracetamol molecule as well as the PDOS graph of O and H atoms in the crystal.

2,4,6-Trinitrophenol (TNP) exists in two crystallographically independent molecules in the unit cell. We study the density of state (DOS), band structure (BS), atomic orbit projected density of state (PDOS) of TNP crystal using a cell containing 152 atoms. The structural parameters of two forms molecules in the bulk and the isolated molecule in a gaseous phase are compared, the band structure nearby the Fermi level, the total DOS and the PDOS of N, H, O, and C atomic orbit are presented. We show that the structure of TNP crystal possesses C–NO…HO–C intramolecular hydrogen-bonding by studying the PDOS graph of O and H atoms in the crystal.

We present density functionary theory (DFT) calculations on the structural parameters and electronic structure for iridium nitride by using the generalized gradient approximation (GGA) and the Perdew–Burke–Ernserhof (PBE) exchange-correlation functional. The lattice parameters and bulk modulus (B0) for the ground state are obtained, and the energy band structure and electron densities of states (DOS) of IrN2 are presented. It is found that IrN2 has a very close indirect energy gap. There is a strong covalent bond between the two nearest N atoms. This gives rise to a very high elastic modulus of IrN2 and reveals the quasimolecular nature of the N2 in IrN2 crystal. Lattice parameters, bulk modulus, and the electronic structure of IrN2 under high pressure have also been investigated based on DFT. The compressibility along three cell vectors is very close to each other. The band gap increases a little with the pressure even when the pressure is up to 100 Gpa.

A theoretical study of electronic properties of the monoclinic DATB is performed using density-functional theory (DFT). The band structure (BS) and the total density of state (TDOS) are presented. The bands of DATB crystal are very flat with energy gap about 2.0 eV, indicating that overlap between orbitals on neighboring molecule is limited. The atomic orbit projected density of state (PDOS) from p-type orbit of C, N, O and s-type orbit of H are addressed. It shows that the structure of DATB crystal possesses C–NO···HN–C and C–NO···H–C intramolecular hydrogen-bonding by analyzing the PDOS. The Mulliken population analysis on atomic charges is also discussed.

Noble metal nanoparticles can modify the optical properties of graphene. Here we present a detailed theoretical analysis of the coherent resonance of quantum plasmons in the graphene–gold cluster hybrid system by using time dependent density functional theory (TDDFT). This plasmon coherent effect is mainly attributed to the electromagnetic field coupling between the graphene and the gold cluster. As a result, the optical response of the hybrid system exhibits a remarkably strong, selectable tuning and polarization dependent plasmon resonance enhanced in wide frequency regions. This investigation provides an improved understanding of the plasmon enhancement effect in a graphene-based photoelectric device.

The hydrogen spillover mechanism, including the H chemisorption, diffusion, and H2 associative desorption on the surface of COFs and H atoms migration from metal catalyst to COFs, have been studied via density functional theory (DFT) calculation. The results described herein show that each sp2 C atom on COFs' surface can adsorb one H atom with the bond length dC–H between 1.11 and 1.14 Å, and the up-down arrangement of the adsorbed H atoms is the most stable configuration. By counting the chemisorption binding sites for these COFs, we can predict the saturation storage densities. High hydrogen storage densities show that the gravimetric uptakes of COFs are in the range of 5.13–6.06 wt%. The CI-NEB calculations reveal that one H atom diffusing along the C–C path on HHTP surface should overcome the 1.41–2.16 eV energy barrier. We chose tetrahedral Pt4 cluster and HHTP as the representative catalyst and substrate, respectively, to study the H migration from metal cluster to COFs. At most, two H atoms can migrate from Pt4 cluster to HHTP substrate. The migration reaction is an endothermic process, undergoing an activation barrier of 1.87 eV and 0.57 eV for the first and second H migration process, respectively. Three types of H2 associative desorption from hydrogenated COFs were studied: (I) the two H adatoms recombining to one H2 molecule with a recombination barrier of 4.28 eV, (II) the abstraction of adsorbed H atoms by gas-phase hydrogen atoms through ER type recombination reactions with a recombination barrier of 1.05 eV, (III) the H2 desorption through the reverse spillover mechanism with an energy barrier of 2.90 eV.

Applying density functional theory (DFT) calculations, we have designed fullerenes (C20, C24, C26, C28, C30, C36, C60 and C70) intercalated phthalocyanine covalent organic frameworks (Cn-Pc-PBBA COFs). First principles molecular dynamics (MD) simulations showed that the structures of Cn-Pc-PBBA COFs are stable at room temperature and even at higher temperature (500 K). The interlayer distance of Pc-PBBA COF has been expanded to 7.48–13.25 Å by the intercalated fullerenes, and the pore volume and surface area were enlarged by 2.3–3.1 and 2.0–2.6 times, respectively. The grand canonical Monte Carlo (GCMC) simulations show that our designed Cn-Pc-PBBA COFs exhibit a superior hydrogen storage capability: at 77 K and P = 100 bar, the hydrogen gravimetric and volumetric uptakes reach 9.4–12 wt% and 48.1–52.2 g L−1, respectively. To meet the requirement for practical application in hydrogen storage, we use the Li-doping method to modify the hydrogen storage performance of Cn-Pc-PBBA COFs. Our results show that the Li atoms can stably locate on the surface of C30-, C36, C60 and C70-Pc-PBBA COFs. At T = 298 K and P = 100 bar, for these four Li-doped Cn-Pc-PBBA COFs, the gravimetric and volumetric uptakes of H2 reach 4.2 wt% and 18.2 g L−1, respectively.

Four types of tetraphenyl silsesquioxane based covalent-organic frameworks (sil-COFs) were designed with the ctn and bor net topologies using molecular mechanics. The computed results revealed that these sil-COFs possess excellent structural properties, such as high porosity (89–95%) and large H2 accessible surface area (5476–6331 m2 g−1), which is advantageous to hydrogen storage. The H2 adsorption isotherms of these sil-COFs were simulated using the grand canonical Monte Carlo (GCMC) method at 77 K and 298 K. The simulated results indicated that at 77 K, sil-COF-4 has the highest gravimetric hydrogen storage capacity of 36.82 wt%, while sil-COF-1 has the highest volumetric hydrogen storage capacity of 63.53 g L−1. At 298 K, sil-COF-4 has the highest gravimetric hydrogen uptake of 5.50 wt%, which already exceeds the U.S. Department of Energy's goal (4.5 wt%) for 2017 and is also very close to the criterion of 6 wt% for practical applications of hydrogen at room temperature. In addition, two possible schemes are proposed to synthesize the sil-COFs.

A new class of 3D adamantane-based aromatic framework (AAF) with diamond-like structure was computationally designed with the aid of density functional theory (DFT) calculation and molecular mechanics (MM) methods. The hydrogen storage capacities of these AAFs were studied by the method of grand canonical Monte Carlo (GCMC) simulations. The calculated pore sizes of three AAFs reveal that AAF-1 and AAF-2 belong to microporous materials, while AAF-3 is a member of mesoporous materials. The GCMC results reveal that at 77 K and 100 bar, AAF-3 exhibits the highest gravimetric hydrogen uptake of 29.50 wt%, while AAF-1 shows the highest volumetric hydrogen uptake of 63.04 g L−1. In particular, the gravimetric hydrogen uptake of AAF-3 reaches the Department of Energy's target of 6 wt% at room temperature. The extraordinary performances of these new AAFs in hydrogen storage have made them enter the list of top hydrogen storage materials up to now.