Linghu Rong-Feng

Evidence of the stability of Mo2TiAlC2 from first principles calculations and its thermodynamical and optical properties

The elastic, thermodynamic, and optical properties of Mo_{2}TiAlC_{2} are investigated by first-principles calculations. Our results indicate that the a axis is stiffer than c axis within 0~100 GPa. Elastic constants calculations predict the large stability range of Mo_{2}TiAlC_{2} under pressure. Several important thermodynamic properties are discussed detailedly, including the Debye temperature, thermal expansion coefficient, and heat capacity etc. The bonding properties are studied from the elastic quantities and electronic properties. The electronic properties are investigated, including the energy band structure, density of states, and so on. The evidence of the instability of Mo_{3}AlC_{2} and stability of Mo_{2}TiAlC_{2} are successfully obtained.

First-Principles Study of Structural, Elastic and Electronic Properties of OsSi

First-principles study of structural, elastic, and electronic properties of the B20 structure OsSi has been reported using the plane-wave pseudopotential density functional theory method. The calculated equilibrium lattice and elastic constants are in good agreement with the experimental data and other theoretical results. The dependence of the elastic constants, the aggregate elastic modulus, the deviation from the Cauchy relation, the elastic wave velocities in different directions and the elastic anisotropy on pressure have been obtained and discussed. This could be the first quantitative theoretical prediction of the elastic properties under high pressure of OsSi compound. Moreover, the electronic structure calculations show that OsSi is a degenerate semiconductor with the gap value of 0.68 eV, which is higher than the experimental value of 0.26 eV. The analysis of the PDOS reveals that hybridization between Os d and Si p states indicates a certain covalency of the Os-Si bonds.

Magnetic moment collapse induced axial alternative compressibility of Cr2TiAlC2 at 420 GPa from first principle

The electronic structure and thermodynamical properties of Cr2TiAlC2 are studied by first principles under pressure. The obtained results observed that the ferromagnetic order is the most stable ground state and the magnetic moment will collapse at about 50 GPa. As a result, the lattice a axis becomes stiffer above about 420 GPa, ultimately presenting the same axial compressibility trends with those of nonmagnetic compounds Mo2TiAlC2 and hypothetical Cr2TiAlC2. The elastic constants and phonon dispersion curves demonstrate the structural stability during the disappearance of magnetic moment and occurrence of axial alternative compressibility. The density of states and energy band calculations confirmed the existence of magnetic moment of Cr2TiAlC2 at 0 GPa and disappearance at high pressures above 50 GPa. Evolutions of magnetic moment collapse with pressure are confirmed by a variety of properties. The obtained grüneisen parameter and thermal expansion coefficients show the maximum value among the known MAX phases, to date and to the author’s knowledge.

Structures and phase transitions of ScH3 under high pressure

The structures and the phase transitions of ScH3 under high pressure are investigated using first-principles calculations. The calculated structural parameters at zero pressure agree well with the available experimental data. With increasing pressure, the transition sequence hcp (GdH3-type)→C2/m→fcc→hcp (YH3-type)→Cmcm of ScH3 is predicted first; the corresponding transition pressures at 0 K are 23 GPa, 25 GPa, 348 GPa, and 477 GPa, respectively. The C2/m symmetry structure is a possible candidate but not a good one as the intermediate state from hexagonal to cubic in ScH3. On the other hand, via the analysis of the structures of hexagonal ScH2.9, cubic ScH3, and cubic ScH2, we find that the repulsive interactions of H—H atoms must play an important role in the transition from hexagonal to cubic.

Interactional potential of helium atom and hydrogen halide molecules

According to ab initio calculations, the differential scattering cross sections between He and HF, HCl, HBr are calculated and compared with experimental data. The results show that the calculation method can calculate comparatively accurate interactional potential. As halogen atom radius increases, at 0 degrees, the minimum of interactional potential shallows, the position of potential well moves into the distance, and anisotropic property becomes prominent, while at 180 degrees, the minimum of interactional potential depens, the position of potential well moves into the distance, and the isotropic property becomes obvious. The potential well depth under T structure is larger than that of linear structure. With the increases of halogen atoms radius, a more spherical symmetry is exhibited, and it can be seen obviously that contributions of radial coefficients V-0, V-1, V-2, V-3, ... decrease gradually, which is important to understand the study of excited state dynamics.

Study on High-Temperature Spectra of Asymptotic Asymmetric-Top Molecule O3

The line intensities of 001-000 transition of the asymptotic asymmetric-top O3 molecule at several temperatures are calculated by directly calculating the partition functions and regarding the rotationless transition dipole moment squared as a constant. The calculated values of the total internal partition sums (TIPS) are consistent with the data of HITRAN database with −0.61% at 296 K. The calculated line intensity data at 500 K and 3000 K are also in excellent agreement with the data in HITRAN database with less than 0.659% and 5.458% at 500 K and 3000 K, which provide a strong support for the calculations of partition function and line intensity at high temperature. Then we extend the calculation to higher temperatures. The line intensities and simulated spectra of ν3 band of the asymptotic asymmetric-top O3 molecule at 4000 and 5000 K are reported. The results are of significance for the studying of the molecular high-temperature spectrum including experimental measurements and theoretical calculations.