The hydrogen abstraction reaction H2S + OH → H2O + SH has been studied using the “gold standard” CCSD(T) method along with the Dunning’s aug-cc-pVXZ (up to 5Z) basis sets. For the reactant (entrance) complex, the CCSD(T) method predicts a HSH···OH hydrogen-bonded structure to be lowest-lying, and the other lower-lying isomers, including the two-center three-electron hemibonded structure H2S···OH, have energies within 2 kcal/mol. The similar situation is for the product (exit) complex. With the aug-cc-pV5Z single point energies at the aug-cc-pVQZ geometry, the dissociation energy for the reactant complex to the reactants (H2S + OH) is predicted to be 3.37 kcal/mol, and that for the product complex to the products (H2O + SH) is 2.92 kcal/mol. At the same level of theory, the classical barrier height is predicted to be only 0.11 kcal/mol. Thus, the OH radical will react promptly with H2S in the atmosphere. We have also tested the performance of 29 density functional theory (DFT) methods for this reaction. Most of them can reasonably predict the reaction energy, but the different functional give quite different energy barriers, ranged from −10.3 to +2.8 kcal/mol, suggesting some caution in choosing density functionals to explore the PES of chemical reactions.

The hydrogen abstraction reaction H2S + OH → H2O + SH has been studied using the “gold standard” CCSD(T) method along with the Dunning’s aug-cc-pVXZ (up to 5Z) basis sets. For the reactant (entrance) complex, the CCSD(T) method predicts a HSH···OH hydrogen-bonded structure to be lowest-lying, and the other lower-lying isomers, including the two-center three-electron hemibonded structure H2S···OH, have energies within 2 kcal/mol. The similar situation is for the product (exit) complex. With the aug-cc-pV5Z single point energies at the aug-cc-pVQZ geometry, the dissociation energy for the reactant complex to the reactants (H2S + OH) is predicted to be 3.37 kcal/mol, and that for the product complex to the products (H2O + SH) is 2.92 kcal/mol. At the same level of theory, the classical barrier height is predicted to be only 0.11 kcal/mol. Thus, the OH radical will react promptly with H2S in the atmosphere. We have also tested the performance of 29 density functional theory (DFT) methods for this reaction. Most of them can reasonably predict the reaction energy, but the different functional give quite different energy barriers, ranged from −10.3 to +2.8 kcal/mol, suggesting some caution in choosing density functionals to explore the PES of chemical reactions.

•Particle swarm optimization method was adopted to search isomers of (H2O)7+ cluster.•Fifteen lower energy isomers were obtained at the MP2 level.•Relationship between isomers’ structures and their energy ordering was analyzed.•Simulated infrared spectra of the lower energy isomers were experimentally demonstrated.•Topological analysis on the four lowest energy clusters were carried out.The structures of the ionized water cluster (H2O)7+ are investigated through the particle swarm optimization method combined with ab initio method. Some new lower energy structures are found after geometric optimization at the MP2/aug-cc-pVDZ level when compared with previous report. We studied the effect of the zero point vibrational energies on the relative energy order of these isomers, the relationship between their schemes and their relative energies, and the composition of their foremost molecular orbitals. The relative free energies of (H2O)7+ isomers below 350 K, the infrared spectra of five lowest energy isomers, and their electronic characteristics were discussed in detail, respectively. Based on topological analysis and reduced density gradient analysis, we find that the interaction between H3O+ core and water molecules is stronger than the interaction between OH radical and water molecules by comparing the structural and the bonding strengths within these cationic water clusters.Download high-res image (69KB)Download full-size image

•The electronic structure calculations with DFT-D and SCC-DFTB of RDX showed consistent results with the experiment.•IR spectrum is obtained by analyzing the trajectory of molecule motion from the MD simulation in CP2K software.•The IR spectra and thermodynamics properties of RDX are used to understand accurately the phase transition behavior of α-RDX converts to γ-RDX at 4 GPa.In present letter, based on density functional theory plus dispersion (DFT-D) and a self-consistent charge density-functional tight-binding (SCC-DFTB) method, the structural and electronic properties are reported, and the phase transition are investigated by analyzing its thermodynamics properties and IR spectrum of RDX. The anisotropy of α- and γ-RDX were discussed at 0–10 GPa. By fitting the third-order Birch–Murnaghan equation of states, the bulk modulus and its pressure derivative of RDX were determined. The α-RDX phase is found stable at ambient condition, however, under pressures, both the values of lattice constants a, b, c and the ΔEvdw at around 4 GPa show abrupt changes which indicate a structural transition occurred. By analyzing the linear compressibility of a, b, c axes at 0–8 GPa, one clearly see that the molecules in α-RDX phase underwent rotations and translational motion to their position in the γ-RDX phase at about 4 GPa, which validates the α–γ phase transition. The IR spectra of α-form and γ-form RDX was calculated by analyzing the trajectory of molecules motion, which also show the phase transition from the spectra changes. Employing the quasi-harmonic Debye model, the enthalpy and specific heat were investigated at various pressures of both phases. The condition of equal enthalpies in both phases also indicates the phase transition of α-form to γ-form at around 4 GPa. The variation of specific heat with temperature approaches to the classical Dulong–Petit's law at high temperature, while at low-temperature it obeys the Debye's T3 law.Enthalpy depends on pressure of RDX. Enthalpy variation depends on pressure for γ-phase relative to that of α-phase (in the top left corner). The ΔEvdw depend on pressure of α-RDX is also inserted in the bottom right corner.

•By using the modified Becke-Johnson (mBJ) exchange functional within the density functional theory (DFT), we have calculated the total energies of the ferromagnetic (FM) and three antiferromagnetic (AFM) orderings of monoclinic BiMnO3, finding that the crystal structures stabilizes in magnetic ground state (FM).•Compared with previous DFT results, our mBJ calculated semiconductor gap, magnetic moment, and other aspects of the electronic structure, are in good agreement with recent experimental values.•The mBJ approach are useful to study similar Bi-based perovskite oxide materials for applications.Recent temperature-dependent x-ray diffraction and Raman spectroscopy experiment proved that single-crystalline BiMnO3 assumes a centrosymmetric monoclinic structure (C2/c space group). Here we investigate magnetic structure and electronic structure of this centrosymmetric BiMnO3 phase by using the modified Becke-Johnson (mBJ) exchange functional within the density functional theory (DFT). Our mBJ calculated semiconductor gap, magnetic moment, and other aspects of the electronic structure, in contrast with previous DFT results, are in good agreement with recent experimental values. This satisfactory description of the electronic structure and magnetism of the BiMnO3 is because mBJ reasonably captures the kinetic property and correlation of electrons. Our calculated results with mBJ approach are both useful to study such Bi-based perovskite oxide materials for spintronics applications.

The structures of cationic water clusters (H2O)8+ have been globally explored by the particle swarm optimization method in combination with quantum chemical calculations. Geometry optimization and vibrational analysis for the 15 most interesting clusters were computed at the MP2/aug-cc-pVDZ level and infrared spectrum calculation at MPW1K/6-311++G** level. Special attention was paid to the relationships between their configurations and energies. Both MP2 and B3LYP-D3 calculations revealed that the cage-like structure is the most stable, which is different from a five-membered ring lowest energy structure but agrees well with a cage-like structure in the literature. Furthermore, our obtained cage-like structure is more stable by 0.87 and 1.23 kcal/mol than the previously reported structures at MP2 and B3LYP-D3 levels, respectively. Interestingly, on the basis of their relative Gibbs free energies and the temperature dependence of populations, the cage-like structure predominates only at very low temperatures, and the most dominating species transforms into a newfound four-membered ring structure from 100 to 400 K, which can contribute greatly to the experimental infrared spectrum. By topological analysis and reduced density gradient analysis, we also investigated the structural characteristics and bonding strengths of these water cluster radical cations.

We investigate the contact geometry and electronic transport properties of a GaN pair sandwiched between Au electrodes by performing density functional theory plus the non-equilibrium Green's function method. The Au–GaN–Au junction breaking process is simulated. We calculate the corresponding cohesion energy and obtain the equilibrium conductance and the projected density of states of junctions. We also calculate the pulling force of the four configurations, and the spatial electron density difference after the junction is broken. In addition, the current of junctions is computed under small bias. It is found that all junctions have large conductance showing a non-linear I–V relationship.

•The elastic properties of AlFe2B2 are theoretically investigated for the first time.•The obtained elastic constants indicated that AlFe2B2 is mechanically stable but anisotropic.•Our results revealed that AlFe2B2 is metallic and magnetic, which is brittle and a covalent–ionic crystal.The structural, electronic, and elastic properties of AlFe2B2 are investigated by first-principles calculations within the generalized gradient approximation. Our results reveal that AlFe2B2 is metallic and magnetic. The magnetic moments of the constituted elements are obtained and their origins are revealed. The computed elastic constants indicate that AlFe2B2 is mechanically stable but anisotropic, which is further confirmed by the shear anisotropic factor, direction-dependent bulk modulus and Young’s modulus. The calculated bulk modulus and shear modulus of AlFe2B2 are greater than these of FeAl, confirming the hardness-enhancement effect of boronizing. The calculated ratio B/G is 0.23 indicating that AlFe2B2 is brittle, and the obtained Poisson ratio is 0.23 implying that AlFe2B2 is a covalent–ionic crystal. These agree with the analyses performed on the partial density of states and Mulliken population. In addition, the velocities of acoustic waves are also computed, which ultimately gives a value of 764 K for the Debye temperature.Graphical abstractsCharge density of AlFe2B2 in (a) the (0 0 1) plane, (b) the (1 0 0) plane and (c) the spin density of the (1 0 0) plane (unit: e/Å3).

Molecular dynamics simulations in conjunction with multiscale shock technique (MSST) are performed to study the initial chemical processes and the anisotropy of shock sensitivity of the condensed-phase HMX under shock loadings applied along the a, b, and c lattice vectors. A self-consistent charge density-functional tight-binding (SCC-DFTB) method was employed. Our results show that there is a difference between lattice vector a (or c) and lattice vector b in the response to a shock wave velocity of 11 km/s, which is investigated through reaction temperature and relative sliding rate between adjacent slipping planes. The response along lattice vectors a and c are similar to each other, whose reaction temperature is up to 7000 K, but quite different along lattice vector b, whose reaction temperature is only up to 4000 K. When compared with shock wave propagation along the lattice vectors a (18 Å/ps) and c (21 Å/ps), the relative sliding rate between adjacent slipping planes along lattice vector b is only 0.2 Å/ps. Thus, the small relative sliding rate between adjacent slipping planes results in the temperature and energy under shock loading increasing at a slower rate, which is the main reason leading to less sensitivity under shock wave compression along lattice vector b. In addition, the C–H bond dissociation is the primary pathway for HMX decomposition in early stages under high shock loading from various directions. Compared with the observation for shock velocities Vimp = 10 and 11 km/s, the homolytic cleavage of N–NO2 bond was obviously suppressed with increasing pressure.

Carbohydrates play a key role in biology, medicine, nanotechnology, and energy storage. However, the physics underlying the interaction between nanomaterials and carbohydrates is still unclear. In this study, we analyzed the interaction of the graphene-on-Al(111) composite with d-glucopyranose. It was observed that the d-glucopyranose molecule can be steadily adsorbed on the surface of the graphene-on-Al(111) composite. The mechanism of this stable adsorption was revealed by the local charges in the graphene induced by the polar group in d-glucopyranose when they are close to each other. Simulated scanning tunneling microscopy (STM) images of d-glucopyranose on the surface of the graphene-on-Al(111) composite, as application of this nanomaterial, show that the gg conformations of d-glucopyranose can be distinguished from the other conformations via the STM technique as a result of the interaction of the graphene-on-Al(111) composite with d-glucopyranose. Therefore, the graphene-on-Al(111) composite is expected to be a potential nanomaterial for detecting single biomolecules. The findings of this study greatly contribute to the fields of nanomaterials and biotechnology, including the development of high-accuracy bioedvices and biosensors.

Cation−π or cation−π–π interaction between one cation and one or two structures bearing rich π-electrons (such as benzene, aromatic rings, graphene, and carbon nanotubes) plays a ubiquitous role in various areas. Here, we analyzed a new type interaction, cation⊗3π, whereby one cation simultaneously binds with three separate π-electron-rich structures. Surprisingly, we found an anomalous increase in the order of the one-benzene binding strength of the cation⊗3π interaction, with K+ > Na+ > Li+. This was at odds with the conventional ranking of the binding strength which usually increases as the radii of the cations decrease. The key to the present unexpected observations was the cooperative interaction of the cation with the three benzenes and also between the three benzenes, in which a steric-exclusion effect between the three benzenes played an important role. Moreover, the binding energy of cation⊗3π was comparable to cation⊗2π for K+ and Na+, showing the particular importance of cation⊗3π interaction in biological systems.

We have performed quantum-based multiscale simulations to study the initial chemical processes of condensed-phase octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) under shock wave loading. A self-consistent charge density-functional tight-binding (SCC-DFTB) method was employed. The results show that the initial decomposition of shocked HMX is triggered by the N–NO2 bond breaking under the low velocity impact (8 km/s). As the shock velocity increases (11 km/s), the homolytic cleavage of the N–NO2 bond is suppressed under high pressure, the C–H bond dissociation becomes the primary pathway for HMX decomposition in its early stages. It is accompanied by a five-membered ring formation and hydrogen transfer from the CH2 group to the −NO2 group. Our simulations suggest that the initial chemical processes of shocked HMX are dependent on the impact velocity, which gain new insights into the initial decomposition mechanism of HMX upon shock loading at the atomistic level, and have important implications for understanding and development of energetic materials.

•Self-consistent ab initio lattice dynamics has been applied to investigate the elastic properties of iron at inner core conditions.•We demonstrate that the vibrational contribution plays a crucial role to stabilize the systems with cubic symmetry.•The seismological data can be explained sufficiently when the crystals of hcp and fcc iron are conglomerated with different orientation.The stability of iron has been reevaluated by a simple but accurate scheme. A combination of self-consistent ab initio lattice dynamics (SCAILD) and the long-wave limit approximation has been applied to investigate the elastic properties of iron at inner core conditions. We demonstrate that the vibrational contribution plays a crucial role to stabilize the systems with cubic symmetry. Especially, the fcc iron will be more stable than hcp iron at the temperature above 7200 K. As for the effect of the anharmonic part, in our calculation the smaller elastic constants are obtained at high temperature compared with previous calculations. Finally, applying our results to the seismological explorations, we find that the seismological data can be explained sufficiently when conglomerating the crystal of hcp and fcc iron with different orientation of fast crystallographic axes.

Chemical functionalization is an effective means of tuning the electronic and crystal structure of a two-dimensional material, but very little is known regarding the correlation between thermal transport and chemical functionalization. Based on the first-principles calculation and an iterative solution of the Boltzmann transport equation, we find that antimonene is a potential excellent thermal material with relatively low thermal conductivity k, and furthermore, chemical functionalization can make this value of k decrease greatly. More interestingly, the origin of the reduction in k is not the anharmonic interaction but the harmonic interaction from the depressed phonon spectrum mechanism, and for some chemical functional atom in halogen, flat modes appearing in the low frequency range play also a key factor in the reduction of k by significantly increasing the three-phonon scattering channels. Our work provides a new view to adjust thermal transport which can benefit thermal material design, and analyzes the reduction mechanism in k from the chemical functionalization of antimonene.