The rapid development of miniaturized electronic devices has aroused intense interest in one-dimensional (1D) nanostructures research. Silicon carbide (SiC) owns abundant 1D geometrical structures, but little is known about their electronic transport properties. Hence, we conduct the systematic study of the electronic transport behavior of (SiC)n (n = 1–4) molecular linear chain, based on the density functional theory and nonequilibrium Green’s function formalism. Results reveal that the conductance of SiC chain is highly sensitive to the local atomic rearrangement, and n is also an important factor to affect their transport properties: the longer the SiC chain, the higher localization of the frontier molecular orbitals and the deeper suppression in transmission spectrum which gives the lower equilibrium conductance and the current. Current–voltage curve of SiC chains exhibit nonlinearity, implying their semiconductor characteristics. The rectifying ratios increase with n which reflect their asymmetric built-in structures and unequal coupling to Au surfaces. Additionally, by analyzing their projected densities of states, we find that px and py orbitals from Si and C atoms make a major contribution to electronic transport channel. Our theoretical studies are expected to provide more fundamental and comprehensive information for further research of the SiC linear chains.

•A pressure-dependent embedded-atom-method potential for tungsten is introduced.•The melting curves of tungsten is consistent well with experimental data.•Radial distribution functions g(r) of tungsten are studied during melting.A pressure-dependent embedded-atom-method (PDEAM) potential for the body-centered cubic (bcc) tungsten (W) is introduced in the pressure range of 0–400 GPa, which makes the P-V/V0 curve of bcc W in highly consistent with the experimental data. It is found that all the pressure-dependent parameters for repulsive core-core interaction term (c0, c1, c2, c3, c4 and c) increase first and become constants later, while the pressure-dependent parameters for n-body term (A and d) decrease first before they tend to constants. The reliability of our PDEAM potential is confirmed by studying the lattice constant, elastic constants, cohesive energy, vacancy formation energy, structural stabilities, zero pressure melting point, and the equation of states of the bcc W. With the PDEAM potential, we determined the melting curves, self-diffusion coefficients of liquid W along the melting curve, and entropies of fusion of the bcc W over a wide pressure range. Moreover, we obtained the structural properties of W including the variations of radial distribution functions g(r) during melting and with increasing pressure.Applied the pressure-dependent embedded-atom-method potential of W, the calculated melting curves is consistent more well with the experimental data.Download high-res image (91KB)Download full-size image

•Particle swarm optimization method was used to search isomers of (H2O)9+ cluster.•Sixteen lower energy isomers of four types were obtained at the MP2 level.•Simulated infrared spectra of (H2O)9+ of the lower energy isomer were experimentally verified.•The interaction between the H3O+ core and water molecules is studied.The 16 lowest energy isomers of cationic water cluster (H2O)9+ have been comprehensively searched by the particle swarm optimization algorithm combined with quantum chemistry calculations. Geometric optimization and vibration analysis of the interesting isomers were made in the MP2/aug-cc-pVDZ level. Our results show that cage structure is the most stable at low temperatures. The relative Gibbs free energy below 400 K was calculated, which indicates that the stability of the cage structure decreases as the temperature increases while the energy of ring is relatively slow. We also illustrate the computationally simulated IR spectra obtained at six different calculated levels and individual IR spectroscopy for seven isomers. The obtained molecular orbits of six representative isomers show good agreement with experiment. Finally, through the topological analysis and density gradient analysis, we compared the interaction between the H3O+ core and H2O as well as the OH radicals.Download high-res image (100KB)Download full-size image

•A wonderful diversity of C10 configuration has been explored by the particle swarm optimization method.•The symmetry of the ground state monocyclic structure and the existence of the linear structure are proved.•The contribution of delocalized electrons to the π-aromaticity is identical for D10h and D5h configuration in the planar C10 system.•The monocyclic C10 clusters is recognized as a globally doubly (σ- and π-) aromatic compound by the AdNDP and CMO analysis.The predicted lower energy structures of neutral carbon cluster C10 are presented by using the particle swarm optimization method in combination with quantum chemistry calculation. Our results describe a wonderful diversity of C10 configuration with the DFT and MP2 methods. For linear and cyclic clusters, the energy of most stable monocyclic structure with D5h symmetry is lower by 1.38 kcal/mol than the transition isomers with D10h symmetry at CCSD(T)/cc-pVTZ level, which is consistent with the previous theoretical results by others. All linear structures of C10 cluster have been certified as the metastable states at different calculation methods in this work. Simulated infrared spectra reveals that the extensive electron localization exists in the D10h configuration leading to the decreasing of the number of vibration modes compared with D5h configuration. The nucleus independent chemical shift (NICS) calculations indicate that planar C10 system is a stable aromatic compound and the position used to calculate the aromatic indices can be affected by the most shielding or deshielded location that we employed. The contribution of the delocalized electrons to the π-aromaticity is identical in C1a and C1b. By the adaptive natural density partitioning (AdNDP) and canonical molecular orbital (CMO) analysis, we know that the highly symmetric structures have more energy degenerate CMOs and 2 center-2 electron bond connection, and monocyclic C10 cluster is a globally doubly (σ- and π-) aromatic compound. Topological analysis and natural bond orbital (NBO) analysis show that there isn’t any electrostatic type of interactions in C10 structures, and much of negative natural valence electron configuration comes from high angular momentum orbitals. According to the electron configurations, the natural hybrid orbital is mainly composed of sp hybrid in the systems. It is worth mentioning that the competition of complicated many-body effects plays a significant role in stabilizing the distorted configuration of C10 cluster. We expect our work can provide more information for further experimental studies.In this work, the symmetry of the ground state monocyclic structure and the existence of the linear structure are proved by the particle swarm optimization method in combination with quantum chemistry calculation. The above picture shows the delocalization result of the adaptive natural density partitioning (AdNDP) π- and σ-bonding pattern for the most stable structure of C10 clusters with the D10h and D5h symmetry. The contribution of delocalized electrons to the π-aromaticity is identical for D10h and D5h configuration in the planar C10 system. The results reveal that the monocyclic C10 clusters is recognized as a globally doubly (σ- and π-) aromatic compound by AdNDP and canonical molecular orbital analysis. There nonexistence of electrostatic type of interactions in C10 structures, and much of negative natural valence electron configuration come from high angular momentum orbitals.Download high-res image (75KB)Download full-size image

•The calculated elastic properties for NbAs, TaP and NbP are obtained for the first time.•MX (M = Ta or Nb; X = As or P) exhibit distinct elastic anisotropy, especially for TaAs and NbAs.•Their phonon frequencies at gamma point, main atomic displacement patterns, phonon velocities, and thermodynamic properties are also presented.We present a comparative investigation on structural, elastic, dynamical and thermodynamic properties of Weyl semimetals MX (M = Ta or Nb; X = As or P) using density functional theory (DFT) within the generalized gradient approximation. The elastic properties of NbAs, TaP and NbP are obtained for the first time, then we compared them with each other and with some well-studied materials. Among four Weyl semimetals, TaP and NbAs possess the largest and smallest bulk modulus B, shear modulus G, and Young's modulus E, respectively, while NbP and TaAs own the maximum and minimum elastic Debye temperature. Through the analysis of three dimensional (3D) representations and two dimensional (2D) projections of Young's modulus, MX series exhibit distinct elastic anisotropy, especially for TaAs and NbAs. The calculated phonon dispersions of four Weyl semimetals show no imaginary frequency throughout the Brillouin zone, indicating they are dynamically stable. In addition, compared with other theoretical results, our calculated Brillouin-zone-center frequencies of MX series are more in line with experimental data. Furthermore, Phonon velocities are obtained using phonon spectra, and anisotropic phonon group velocities are responsible for their anisotropic lattice thermal conductivity. Additionally, thermodynamic properties are also predicted using the calculated phonon density of states. The results are in good agreement with available experimental values. We expect our work can provide more information for further experimental studies.

•Including the previous ground state structure a new one has been predicted.•CALYPSO performs well for semiconductor cluster from our results.•We are interested in its Gibbs free energies and quantum effect.The particle swarm optimization method in conjunction with quantum chemical calculations is used to search lower-energy structures for the mixed Ga4As4 semiconductor clusters. Geometry optimization, vibrational analysis, ionization potential, and electron affinity are implemented for the fourteen representative isomers. Our results present a wonderful diversity of Ga4As4 configurations within density functional theory (DFT) level and MP2 level. The relationships between the structural arrangements and their point groups are discussed and the obtained polarizabilities agree well with the latest calculation results. We obtain the lowest-energy structure proposed in previous work and predict a new one. Special attention is paid to their geometry, IR spectra, natural bond orbital (NBO) charge and molecular orbitals to compare them in structure and bonding. According to their relative Gibbs free energies, their energy orders at different temperatures are obtained. The electron densities ρ(r) and its second derivatives ▽2ρ(r) at meaningful bond critical points through topological analysis and NBO charge populations analysis indicate that the dominant interaction among Ga and As atoms is covalent bonding.

•We probed the cubic and hexagonal phases and confirmed the ground state of NiVSb.•The phase transition of NiVSb was investigated for the first time.•We discussed the elastic and thermodynamic properties of the cubic NiVSb.•The paper provides a future reference on electronic properties of the cubic NiVSb.Using the generalized gradient approximation based on ab initio plane-wave pseudopotential density functional theory, we explore the structural, elastic, electronic properties and phase transition of NiVSb. With the help of the quasi-harmonic Debye model, we also investigate the Grüneisen parameter, thermal expansivity, heat capacity and Debye temperature of NiVSb with a cubic structure. Results show that the calculated lattice constants are excellently consistent with the available data of theoretical and experimental studies. And NiVSb in the ground state is predicted to be a half-metal with a gap of 0.38 eV, which grows weaker with pressure increasing. To provide a comparative and complementary study to future researches, we investigated the elastic and thermodynamic properties and phase transition for the first time.

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.

•LiBSi2 shows a semiconductor ground state from GGA calculation.•Directional dependence of Young’s modulus are calculated in different planes.•Elastic properties are investigated under hydrostatic and non-hydrostatic pressure.•Mulliken populations is studied to reveal the crystal’s bonding property.We investigate the structural, elastic and electronic properties of the tetragonal structure LiBSi2 under pressure from first principles in the frame of the density functional theory (DFT). Both local density approximation (LDA) and generalized gradient approximation (GGA) methods are used in our calculation. It is found that, the obtained lattice constants of LiBSi2 under zero pressure and zero temperature from GGA calculations are in better agreement with the available experimental data and other theoretical ones than those from LDA calculations. The hydrostatic (isotropic) pressure and non-hydrostatic (anisotropic) pressure dependences of the elastic constants Cij, bulk modulus B, shear modulus G, elastic anisotropy index AU, AB, AG, Young’s modulus E, Poisson’s ratio σ, aggregate acoustic velocities Vl and Vs, and Debye temperature ΘE of LiBSi2 are also presented. The pressure dependences of the elastic constants C11, C33, C12, and C13 vary largely under the effect of pressure when compared with the variations of C44 and C66. The calculated bulk modulus B from the elastic constants is 99 GPa, which is in agreement with the result obtained from the Vinet equation of state (105.01 GPa) and the result of Zeilinger et al. (103.7 GPa). In addition, GGA calculations give a band gap of 1.19 eV, indicating that the tetragonal structure LiBSi2 is a semiconductor, consistent with the experimental result.Graphical abstract

•Geometrical structures of the Al2Bn- (n = 1−9) clusters are first determined.•Stability of the AlBn- and Al2Bn- (n = 1−9) clusters is investigated systematically.•Dissociate approaches of AlBn- and Al2Bn- (n = 1−9) clusters is first revealed.•Magnetic properties of AlBn- and Al2Bn- (n = 1−9) clusters is studied.The structures and electronic properties of a series small mixed aluminum boron clusters AlBn- and Al2Bn- (n = 1−9) have been investigated systematically with the density functional approach. Results show that the ground state prefers the lowest spin state except Al2B-Al2B- and the Al atom tends to be adsorbed at the surface in both boron–aluminum systems. Moreover, results about the stability indicate clusters AlB8- and Al2B7- have the considerable enhanced stability among the clusters of AlBn- and Al2Bn- (n = 1−9). Besides, the electronic and magnetic properties for two systems are also investigated, and the total magnetic moments as a function of cluster size show a dramatic odd–even alternative behavior for clusters AlBn-, while the addition of one more Al atom makes the total magnetic moments of the clusters Al2Bn- contrary except n = 1.

•The conductance oscillates with a period of two atoms as the number of atoms in the silicon atomic chain is varied.•The transport channel is mainly contributed by px and py orbital electrons of silicon atoms.•The even–odd oscillation is robust under external voltage up to 1.2 V.The conductance of linear silicon atomic chains with n=1–8 atoms sandwiched between Au electrodes is investigated by using the density functional theory combined with non-equilibrium Green's function. The results show that the conductance oscillates with a period of two atoms as the number of atoms in the chain is varied. We optimize the geometric structure of nanoscale junctions in different distances, and obtain that the average bond-length of silicon atoms in each chain at equilibrium positions is 2.15±0.03 Å. The oscillation of average Si–Si bond-length can explain the conductance oscillation from the geometric structure of atomic chains. We calculate the transmission spectrum of the chains in the equilibrium positions, and explain the conductance oscillation from the electronic structure. The transport channel is mainly contributed by px and py orbital electrons of silicon atoms. The even–odd oscillation is robust under external voltage up to 1.2 V.Linear silicon atomic chains with n=1–8 atoms sandwiched between Au electrodes. The conductance oscillates with a period of two atoms as the number of atoms in the chain is varied. The even–odd oscillation is robust under external voltage up to 1.2 V.

We obtained the melting temperatures of the W nanoclusters with diameters in the range of 2.5–5.0 nm which manifest the good linear fitting to the size of nanoclusters (N−1/3). Four different initial configurations at each size produce nearly the same melting points, with the maximum discrepancies less than 40 K. The extrapolated bulk melting point 4210 K is lower than the simulated bulk value 4520 K. Surface premelting is detected by density profiles, deformation parameters and bond orientational order parameters. Moreover, by dividing particles into surface and subsurface layers, we analyzed the different behaviors of the inner and outer shell atoms during melting in detail. During coalescence of W nanoclusters (WN + WN → W2N), the shape change is along the path of peanut → rod-like → spherical → liquid structure. The obtained melting points from W2N are in good agreement with those from WN + WN, indicating that melting temperatures are mainly relevant to the number of atoms, and nearly not affected by the different surface areas in nanoclusters.

We investigate the elastic and electronic structure properties of BaHfN2 under pressure by performing the generalized gradient approximation (GGA) and local density approximation (LDA) correction scheme in the frame of density functional theory (DFT). The pressure dependences of the normalized lattice parameters a/a0 and c/c0, the ratio c/a, and the normalized primitive volume V/V0 of BaHfN2 are also obtained. The obtained lattice constants and bulk modulus agree well with the available experimental and other theoretical data. The pressure dependences of elastic properties are investigated for the first time. It is found that, as the pressure increases, the elastic constants C11, C33, C66, C12 and C13 increase, the variation of elastic constant C44 is not obvious. At 40 GPa, the tetragonal structure BaHfN2 transfers to another structure at zero temperature. Moreover, our compressional and shear wave velocities VL = 5.87 km/s and VS = 3.12 km/s as well as the Debye temperature Θ = 451.7 K at 0 GPa are obtained. The pressure dependences of the band structures, energy gap and density of states are also investigated.Highlights► The lattice constants and bulk modulus of BaHfN2 obtained agree well with the available experimental and other theoretical data. ► The pressure dependences of elastic properties are investigated for the first time. ► At 40 GPa, the tetragonal structure BaHfN2 transfers to another structure at zero temperature. ► The pressure dependences of the compressional and shear wave velocities, band structures, energy gap and density of states are also investigated successfully.

The elastic and thermodynamic properties of the L12 type (Cu3Au) structure Zr3Al intermetallic compound under high pressure and temperature are investigated by using ab initio plane-wave pseudopotential density functional theory (DFT) within the generalized gradient approximation (GGA). The result of the heat of formation of Zr3Al crystal investigated is in consistent with those by others. The elastic properties of the cubic Zr3Al under high pressure are studied for the first time, and we found its elastic modulus, compressional and shear wave velocities are increasing monotonically with increasing pressure. Finally, the thermodynamic properties of the cubic Zr3Al are predicted by using the quasi-harmonic Debye model. The Debye temperature Θ, the bulk modulus B, the heat capacity Cv, and the thermal expansion α are calculated as a function of the pressure and temperature in the ranges of 0–55 GPa and 0–1800 K.Graphical abstractElastic constants, elastic modulus and compressional and shear wave velocities of the L12 type (Cu3Au) structure Zr3Al in this figures are increasing monotonically with increasing pressure.Highlights► The elastic properties of the cubic Zr3Al under high pressure are firstly studied. ► The heat of formation of Zr3Al crystal is in consistent with those by others. ► Elastic constants and modulus and Debye temperature increase linearly with pressure. ► The compressional and shear wave velocities increase monotonically with pressure. ► The thermodynamic properties are predicted by using the quasi-harmonic Debye model.

The melting curves of iron over a wide range of pressures were determined by the molecular dynamics (MD) simulations with the Sutton−Chen version of EAM (embedded atom method). The melting of iron was simulated with two methods, that is, the hysteresis (one-phase) approach and the two-phase approach. Both methods strongly reduced the overheating, and their results are in the close proximity at the applied pressures. The obtained melting curves are consistent with both the diamond anvil cell (DAC) experiments at ambient pressure and the shock wave (SW) measurements at high pressure. During the investigation of the atomic structures of iron, we found a slight increase in the coordination number on melting. When taking account of the ultrapressure melting curves obtained by the Clausius−Clapeyron slope, we found that the starting point is the key to determine the melting curves, and the melting temperatures computed by the Clausius−Clapeyron slope might change dramatically if the initial temperatures change. Finally, the thermal equation of state (EOS) and the pressure dependence of entropy of fusion ΔS of iron have also been obtained.

We obtained the melting temperatures of the W nanoclusters with diameters in the range of 2.5–5.0 nm which manifest the good linear fitting to the size of nanoclusters (N−1/3). Four different initial configurations at each size produce nearly the same melting points, with the maximum discrepancies less than 40 K. The extrapolated bulk melting point 4210 K is lower than the simulated bulk value 4520 K. Surface premelting is detected by density profiles, deformation parameters and bond orientational order parameters. Moreover, by dividing particles into surface and subsurface layers, we analyzed the different behaviors of the inner and outer shell atoms during melting in detail. During coalescence of W nanoclusters (WN + WN → W2N), the shape change is along the path of peanut → rod-like → spherical → liquid structure. The obtained melting points from W2N are in good agreement with those from WN + WN, indicating that melting temperatures are mainly relevant to the number of atoms, and nearly not affected by the different surface areas in nanoclusters.