N2O reduction over hexagonal BN nanosheet: effects of Stone–Wales defect and carbon pair doping

Nitrous oxide (N₂O) adsorption on the pristine and Stone–Wales (SW)-defected hexagonal BN nanosheets were investigated using density functional calculations including dispersion correction. It was found that N₂O is weakly adsorbed on the pristine sheet (h-BN) through van der Waals interaction with adsorption energy of ?1.2 kcal/mol. SW-defected sheet was found to be more reactive toward N₂O molecule having no significant change in electronic properties. However, the formation of B–B and N–N bond pairs in SW-defected sheet can be avoided, if there is a C–C pair doped in sheet (C₂-SW-h-BN). In this case, a strong adsorption is found due to large adsorption energy (?23.7 kcal/mol) and short bond length compared to the SW-h-BN complex. Interestingly, it was indicated that the N₂O molecule could be reduced into the N₂ on the C₂-SW-h-BN.     

Role of sodium decoration on the methane storage properties of BC3 nanosheet

First-principles calculations including dispersion correction are carried out to investigate pristine and Na-decorated graphene-like BC₃ (h-BC₃) for their application as methane storage materials. Structural optimization shows that the methane is physisorbed on the pristine sheet via van der Waals forces with adsorption energy of ?2.7 kcal/mol. It was found that unlike the pristine graphene, sodium decorated sheet can effectively interact with the CH₄ molecule, so that each metal atom bound on sheet may adsorb up to four CH₄. Furthermore, no bond dissociation was observed for the adsorption of CH₄ on Na-decorated h-BC₃, which means that decorated sheet can act as a storage device for methane safety storage. The results indicate that decoration of the Na atom on surface of sheet induces significant changes in electronic properties of the sheet and its E _g is unchanged after adsorption of CH₄ molecules. Theoretical methane storage capacity of Na-decorated BC₃ nanosheet could approach 18.1 wt%.     

Theoretical calculation of the dehydrogenation of ethanol on a Rh/CeO2(111) surface

We applied periodic density-functional theory (DFT) to investigate the dehydrogenation of ethanol on a Rh/CeO2 (111) surface. Ethanol is calculated to have the greatest energy of adsorption when the oxygen atom of the molecule is adsorbed onto a Ce atom in the surface, relative to other surface atoms (Rh or O). Before forming a six-membered ring of an oxametallacyclic compound (Rh-CH2CH2O-Ce(a)), two hydrogen atoms from ethanol are first eliminated; the barriers for dissociation of the O-H and the beta-carbon (CH2-H) hydrogens are calculated to be 12.00 and 28.57 kcal/mol, respectively. The dehydrogenated H atom has the greatest adsorption energy (E(ads) = 101.59 kcal/mol) when it is adsorbed onto an oxygen atom of the surface. The dehydrogenation continues with the loss of two hydrogens from the alpha-carbon, forming an intermediate species Rh-CH2CO-Ce(a), for which the successive barriers are 34.26 and 40.84 kcal/mol. Scission of the C-C bond occurs at this stage with a dissociation barrier Ea = 49.54 kcal/mol, to form Rh-CH(2(a)) + 4H(a) + CO(g). At high temperatures, these adsorbates desorb to yield the final products CH(4(g)), H(2(g)), and CO(g).     

DFT study on the adsorption and dissociation of hydrogen sulfide on MgO nanotube

The adsorption of a H₂S molecule on the surface of an MgO nanotube was investigated using density functional theory. It was found that H₂S molecule can be associatively adsorbed on the tube surface without any energy barrier or it can be dissociated into –H and –SH species overcoming energy barrier of 4.03–7.77 kcal/mol. The associative adsorption is site selective so that the molecule is oriented in such a way that the sulfur atom was linked to an Mg atom. The HOMO–LUMO energy gap of the tube has slightly changed upon associative adsorption, while they were significantly influenced by dissociation process. Especially, the highest occupied molecular orbital of the tube shifts to higher energies which can facilitate electron emission current from the tube surface. Also, energy gap of the tube dramatically decreased by about 0.93–1.05 eV which influences the electrical conductivity of the tube.     

First principle and ReaxFF molecular dynamics investigations of formaldehyde dissociation on Fe(100) surface

Detailed formaldehyde adsorption and dissociation reactions on Fe(100) surface were studied using first principle calculations and molecular dynamics (MD) simulations, and results were compared with available experimental data. The study includes formaldehyde, formyl radical (HCO), and CO adsorption and dissociation energy calculations on the surface, adsorbate vibrational frequency calculations, density of states analysis of clean and adsorbed surfaces, complete potential energy diagram construction from formaldehyde to atomic carbon (C), hydrogen (H), and oxygen (O), simulation of formaldehyde adsorption and dissociation reaction on the surface using reactive force field, ReaxFF MD, and reaction rate calculations of adsorbates using transition state theory (TST). Formaldehyde and HCO were adsorbed most strongly at the hollow (fourfold) site. Adsorption energies ranged from ?22.9 to ?33.9 kcal/mol for formaldehyde, and from ?44.3 to ?66.3 kcal/mol for HCO, depending on adsorption sites and molecular direction. The dissociation energies were investigated for the dissociation paths: formaldehyde → HCO + H, HCO → H + CO, and CO → C + O, and the calculated energies were 11.0, 4.1, and 26.3 kcal/mol, respectively. ReaxFF MD simulation results were compared with experimental surface analysis using high resolution electron energy loss spectrometry (HREELS) and TST based reaction rates. ReaxFF simulation showed less reactivity than HREELS observation at 310 and 523 K. ReaxFF simulation showed more reactivity than the TST based rate for formaldehyde dissociation and less reactivity than TST based rate for HCO dissociation at 523 K. TST‐based rates are consistent with HREELS observation. © 2013 Wiley Periodicals, Inc.     

A theoretical study on the hydrogen storage properties of planar (AlN)<Subscript>n</Subscript> clusters (<Emphasis Type="Italic">n</Emphasis> = 3-5)

The structures and hydrogen storage capacities of (AlN)_n (n = 3-5) clusters have been systematically investigated by using density functional theoretical calculations. At ωB97xD/6-311 + G(d, p) level, the planar structures of (AlN)_n (n = 3-5) can adsorb 6-10 H₂ molecules with average adsorption energies in the range 0.16 to 0.11 eV/H₂, which meet the adsorption energy criteria of reversible hydrogen storage. The gravimetric density of H₂ adsorbed on (AlN)_n clusters can reach 8.96 wt%, which exceed the target set by Department of Energy. The hydrogen adsorption energies with Gibbs free energy correction indicate that the adsorption of 6 H₂ in (AlN)₃, 8 H₂ in (AlN)₄ and 10 H₂ in (AlN)₅ is energetically favorable below 96.48, 61.43, and 34.21 K, respectively. These results are expected to motivate further the applications of clusters to be efficient hydrogen storage materials.     

DFT study of the dissociative adsorption of HF on an AlN nanotube

We have investigated the adsorption of hydrogen fluoride (HF) on the AlN nanotube surface using density functional theory in terms of energetic, structural and electronic properties. By overcoming energy barriers of 27.90–52.30 kcal/mol, HF molecule is dissociated into H and F species on the tube surface and its molecular structure is not preserved after the adsorption process. Dissociation energies have been calculated to be −52.57 and −70.10 kcal/mol. The process has negligible effect on the electronic and field emission properties of the AlN nanotube. This process may increase the solubility of AlN nanotubes.     

Density functional study on the sensing properties of nano-sized BeO tube toward H2S

Using density functional calculations, we have investigated the adsorption of a H₂S molecule on the pristine and Si-doped BeO nanotubes (BeONT). It was found that the H₂S molecule is physically adsorbed on the pristine BeONT with adsorption energies ranging from 3.0 to 4.2 kcal/mol. Substituting a Be or O atom of the tube by Si increases the adsorption energy to 6.9–17.2 kcal/mol. We found that substituting an O atom by Si makes the electronic properties of the BeONT strongly sensitive to the H₂S molecule. Therefore, the process of Si doping provides a good strategy for improving the sensitivity of BeONT to toxic H₂S, which cannot be trapped and detected by the pristine BeONT. Also, the emitted electron current density from the Si_O–BeONT will be significantly increased after the H₂S adsorption.     

Theoretical study of bifurcated hydrogen bonding effects on the 1J(N,H), 1hJ(N,H), 2hJ(N,N) couplings and 1H, 15N shieldings in model pyrroles

According to the density functional theory calculations, the X···H···N (X?N, O) intramolecular bifurcated (three‐centered) hydrogen bond with one hydrogen donor and two hydrogen acceptors causes a significant decrease of the ^1hJ(N,H) and ^2hJ(N,N) coupling constants across the N? H···N hydrogen bond and an increase of the ¹J(N,H) coupling constant across the N? H covalent bond in the 2,5‐disubsituted pyrroles. This occurs due to a weakening of the N? H···N hydrogen bridge resulting in a lengthening of the N···H distance and a decrease of the hydrogen bond angle at the bifurcated hydrogen bond formation. The gauge‐independent atomic orbital calculations of the shielding constants suggest that a weakening of the N? H···N hydrogen bridge in case of the three‐centered hydrogen bond yields a shielding of the bridge proton and deshielding of the acceptor nitrogen atom. The atoms‐in‐molecules analysis shows that an attenuation of the ^1hJ(N,H) and ^2hJ(N,N) couplings in the compounds with bifurcated hydrogen bond is connected with a decrease of the electron density ρ_H···N at the hydrogen bond critical point and Laplacian of this electron density ?²ρ_H···N. The natural bond orbital analysis suggests that the additional N? H···X interaction partly inhibits the charge transfer from the nitrogen lone pair to the σ*_{N? H} antibonding orbital across hydrogen bond weakening of the ^1hJ(N,H) and ^2hJ(N,N) trans‐hydrogen bond couplings through Fermi‐contact mechanism. An increase of the nitrogen s‐character percentage of the N? H bond in consequence of the bifurcated hydrogen bonding leads to an increase of the ¹J(N,H) coupling constant across the N? H covalent bond and deshielding of the hydrogen donor nitrogen atom. Copyright © 2010 John Wiley & Sons, Ltd.     

Hydrogen adsorption on carbon-doped boron nitride nanotube

The adsorption of atomic and molecular hydrogen on carbon-doped boron nitride nanotubes is investigated within the ab initio density functional theory. The binding energy of adsorbed hydrogen on carbon-doped boron nitride nanotube is substantially increased when compared with hydrogen on nondoped nanotube. These results are in agreement with experimental results for boron nitride nanotubes (BNNT) where dangling bonds are present. The atomic hydrogen makes a chemical covalent bond with carbon substitution, while a physisorption occurs for the molecular hydrogen. For the H(2) molecule adsorbed on the top of a carbon atom in a boron site (BNNT + C(B)-H(2)), a donor defect level is present, while for the H(2) molecule adsorbed on the top of a carbon atom in a nitrogen site (BNNT + C(N)-H(2)), an acceptor defect level is present. The binding energies of H(2) molecules absorbed on carbon-doped boron nitride nanotubes are in the optimal range to work as a hydrogen storage medium.     

First-principles Calculations of H2O Adsorption Reaction on the GaN（0001） Surface

The adsorption and decomposition of H2O on GaN（0001） surface have been explored employing density functional theory （DFT）. Two distinct adsorption features of H2O on GaN（0001） corresponding to molecular adsorption and H-OH dissociative adsorption are revealed by our calculations. The activities of the surface reactions of H2O on GaN（0001） surface are investigated. For the stepwise processes of H2O decomposition into H2 in gas phase and adsorbed O atom （H2O（g）→H2O（chem）→OH（chem） ＋ H（chem）→2H（chem） ＋ O（chem）→H2（g） ＋ O（chem））, the first and second steps are facile and can even occur at room temperature; while the last two have high barriers and thus are difficult to proceed, especially the fourth step is endothermic. In short, H2O adsorption and decomposition into H2 in gas phase and adsorbed O atom on GaN（0001） surface are exothermic by -43.98 kcal/mol.     

Density-functional calculations of HCN adsorption on the pristine and Si-doped graphynes

Graphyne, a lattice of benzene rings connected by acetylene bonds, is one-atom-thick planar sheet of sp- and sp²-bonded carbons differing from the hybridization of graphene (considered as pure sp²). Here, HCN adsorption on the pristine and Si-doped graphynes was studied using density-functional calculations in terms of geometric, energetic, and electronic properties. It was found that HCN molecule is weakly adsorbed on the pristine graphyne and slightly affects its electronic properties. While, Si-doped graphyne shows high reactivity toward HCN, and, in the most favorable state, the calculated adsorption energy is about ?10.1 kcal/mol. The graphyne, in which sp-carbon was substituted by Si atom, is more favorable for HCN adsorption in comparison with sp²-carbon. It was shown that the electronic properties of Si-doped graphyne are strongly sensitive to the presence of HCN molecule and therefore it may be used in sensor devices.     

Influence of insertion of a noble gas atom on halogen bonding in H2O···XCCNgF and H3N···XCCNgF (X = Cl and Br; Ng = Ar, Kr, and Xe) complexes

The H₂O···XCCNgF and H₃N···XCCNgF (X = Cl and Br; Ng = Ar, Kr, and Xe) complexes have been studied with quantum chemical calculations at the MP2/aug-cc-pVTZ level. The results show that the inserted noble gas atom has an enhancing effect on the strength of halogen bond, and this enhancement is weakened with the increase of noble gas atomic number. The methyl and Li substituents in the electron donor strengthen the halogen bond. The interaction energy increases from ?3.75 kcal/mol in H₃N–BrCCF complex to ?9.66 kcal/mol in H₂LiN–BrCCArF complex. These complexes have been analyzed with atoms in molecules, natural bond orbital, molecular electrostatic potentials, and energy decomposition calculations.     

Interaction of hydrogen with cerium oxide surfaces: a quantum mechanical computational study

The interaction of the (110) and (111) surfaces of ceria (CeO(2)) with atomic hydrogen is studied with ab initio calculations based on density functional theory. A Hubbard U term added to the standard density functional allows to accurately describe the electronic structure of the two surfaces. The minimum energy configuration for the adsorbed H on each of the two surfaces is obtained. An O-H-O bridge is formed on the (110) surface, whereas an axial tricoordinated OH group results on the (111) surface. For both surfaces, the adsorption of an H atom is accompanied by the reduction of a single Ce ion (which is one of the nearest neighbors of the adsorbed atom) and by a substantial outward protrusion of the O atom(s) directly bound to H. The adsorption of atomic H on the (110) and (111) surfaces is energetically favored by -150.8 and -128.3 kJ/mol, respectively, with respect to free molecular H(2). The calculated frequencies for the OH stretching vibrational mode are 3100 cm(-1) for the (110) surface and 3627 cm(-1) for the (111) surface. The latter value is in excellent agreement with experimental data reported in the literature.     

Si-decorated graphene: a superior media for lithium-ions storage

The characteristics of lithium adsorption on Si-decorated graphene are investigated using first-principles density functional theory calculations. It is found that the Si atom is strongly adsorbed at the bridge site of the C–C bond with binding energy of about ?26.75 kcal/mol. We show that Si decorating turns Si:graphene complex into an electron-deficient system and significantly enhances the Li-storage capacity on the graphene. The obtained results indicate that up to eight Li-ions being adsorbed onto the Si-decorated graphene can form the stable complex. It is found, interestingly, that two Si atoms coated onto double-side of the graphene can strongly adsorb sixteen Li-ions. The analyses of electronic structures show a strong interaction between Li-ions and Si-decorated graphene leading to a high exothermicity. The stability of the sixteen Li-ions adsorbed on the Si:graphene system was evaluated with ab initio molecular dynamics simulation which have been carried out at room temperature. Our first-principles results are relevant to identify the potential applications of Si-decorated graphene as superior media for Li-ions storage.     

Effect of spin polarization for hydrogen adsorbed on Si(111)(1×1) surface: First‐principles calculations

The role of spin polarization on adsorption of atomic and molecular hydrogen on Si(111)(1×1) surface is examined by comparing the results of the local spin density approximation (LSD) and those of the local density approximation (LDA). A large improvement of the adsorption energies (around 0.8 eV/H) was found for the H atom adsorbed on Si(111)(1×1) surface. The inclusion of spin polarization reduces the overbinding between the H atom and the silicon surface and its effect is much more pronounced when the H atom is far away from the surface. Despite of the large changes in the adsorption energies, the main character of the potential energy surface of the H atom on Si(111)(1×1) surface is retained. An opposite effect is found in the charge‐density‐transfer map of LSD results as compared to LDA results for the H atom approaching the surface through the H3 path, in which the H atom loses electrons rather than gains electrons from the surface. The fact that the H atom tends to lose electrons in the silicon bulk has already been reported by the experimental studies for the behavior of the H atom in the p‐type silicon. For the molecular hydrogen on Si(111)(1×1) surface, the effect of the spin polarization is so small that it can be neglected. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 79: 47–55, 2000     

Dynamic factors in the reactions between the magic cluster Al(13)⁻ and HCl/HI

The icosahedral Al is a "magic" cluster with remarkable stability due to its high symmetry and closed valence shells. Its reactivity has provided a molecular model for understanding oxidation and dissolution processes in bulk metals. By first principles calculations, we demonstrated the importance of dynamic factors in the Al + HX reactions, with HX being either HCl or HI. There was a barrier to the dissociative adsorption of HX on the surface of an Al cluster, which involved charge transfer from Al. Furthermore, the H atom could be bonded to the cluster in multiple ways, similar to the top, bridge and hollow adsorption sites on Al(111) surface. With a large amount of energy (～40 kcal mol(-1)) deposited during the formation of Al(13)HX(-), the H atom could easily migrate among these sites, similar to the diffusion of hydrogen on metal surfaces. These factors were therefore important considerations in the formation and dissociation of Al(13)HX(-), and more generally in reactions involving other metal clusters.     

Investigation on the individual contributions of N?H···OC and C?H···OC interactions to the binding energies of β‐sheet models

In this article, the binding energies of 16 antiparallel and parallel β‐sheet models are estimated using the analytic potential energy function we proposed recently and the results are compared with those obtained from MP2, AMBER99, OPLSAA/L, and CHARMM27 calculations. The comparisons indicate that the analytic potential energy function can produce reasonable binding energies for β‐sheet models. Further comparisons suggest that the binding energy of the β‐sheet models might come mainly from dipole–dipole attractive and repulsive interactions and VDW interactions between the two strands. The dipole–dipole attractive and repulsive interactions are further obtained in this article. The total of N? H···H? N and C?O···O?C dipole–dipole repulsive interaction (the secondary electrostatic repulsive interaction) in the small ring of the antiparallel β‐sheet models is estimated to be about 6.0 kcal/mol. The individual N? H···O?C dipole–dipole attractive interaction is predicted to be ?6.2 ± 0.2 kcal/mol in the antiparallel β‐sheet models and ?5.2 ± 0.6 kcal/mol in the parallel β‐sheet models. The individual C^α? H···O?C attractive interaction is ?1.2 ± 0.2 kcal/mol in the antiparallel β‐sheet models and ?1.5 ± 0.2 kcal/mol in the parallel β‐sheet models. These values are important in understanding the interactions at protein–protein interfaces and developing a more accurate force field for peptides and proteins. © 2009 Wiley Periodicals, Inc. J Comput Chem 2010     

Li修饰B12N12储氢行为的密度泛函理论研究

采用基于密度泛函理论(DFT)的第一性原理投影缀加波方法, 研究了Li 修饰的B₁₂N₁₂笼子的储氢行为.计算结果表明: Li 原子吸附在B₁₂N₁₂笼子的四元环和六元环相交的B－N桥位上, 相对于其它六个高对称吸附位置更稳定, B₁₂N₁₂笼子周围最多可以吸附3 个Li 原子, 最稳定的构型是三个Li 原子同时吸附在N原子顶位(Top-N site). 每个Li 原子的周围能吸附三个氢分子, 笼子外侧还可以吸附两个氢分子, 内部最多可以吸附5 个氢分子. 考虑到笼内和笼外的吸附, B₁₂N₁₂笼子总的储氢量(氢分子)达到9.1% (w).