Equation of state for solids considering cohesive energy and anharmonic effect and its application to MgO

A simple equation of state （EOS） in wide ranges of pressure and temperature is constructed within the MieGruneisen Debye framework. Instead of the popular Birch-Murnaghan and Vinet EOS, we employ a five-parameter cold energy expression to represent the static EOS term, which can correctly produce cohesive energy without any spurious oscillations in the extreme compression and expansion regions, We developed a Pade approximation-based analytic Debye quasiharmonic model with high accuracy which improves the performance of EOS in the low temperature region. The anharmonic effect is taken into account by using a semi-empirical approach. Its reasonability is verified by the fact that the total thermal pressure tends to the lowest-order anharmonic expansion in the literature at low temperature, and tends to ideal-gas limitation at high temperature, which is physically correct. Besides, based on this approach, the anharmonic thermal pressure can be expressed in the Griineisen form, which is convenient for applications. The proposed EOS is used to study the thermodynamic properties of MgO including static and shock compression conditions, and the results are very satisfactory as compared with the experimental data.

High-Fidelity Hugoniots of α Phase RDX Solid from High-Quality Force Field with Thermal,Zero-Point Vibration,and Anharmonic Effects

It is shown that the introduction of thermal effect, zero-point vibration, and phonon anharmonicity to a high quality and first-principle-Sased force field （atomic potential） results in a significant improvement in predict- ing the densities for the α phase crystalline hexahydro-1,3,5-trinitro-l,3,5-triazine （RDX）, and derivation of its high-fidelity Hugoniot locus and Mie-Grfineisen equation of state covering a very wide range of pressures and temperatures. This work can be used to efficiently and accurately predict the thermophysical properties of solid explosives over the pressures and temperatures to which they are subjected, which is a long-standing issue in the field of energetic materials.

Anharmonic effect of adiabatic quantum pumping

Based on the scattering matrix approach.we systematically investigate the anharmonic effect of the pumped current in double-barrier strructures with adiabatic time-modulation of two sinusoidal AC driven potential heights. The pumped currem as a functionof the pha.se difference bet ween the two driven potentials looks like to be sinusoidal, but actually it contains sine functions of double and more phase difference, it is found that this kind of anharmonic effect of the pumped current is determined combinedly by the Berry curvature and parameter va.riation loop trajectory. Therefore small ratio of the driving amplitude and the static amplitude is not necessary for harmonic pattern in the pmnped era＇rent, to dominate for smooth Berry curvatureon the surface within the parameter variation loop.

Study on the relationships between Raman shifts and temperature range for α-plane GaN using temperature-dependent Raman scattering

In this paper,Raman shifts of a-plane GaN layers grown on r-plane sapphire substrates by low-pressure metal-organic chemical vapor deposition（LPMOCVD） are investigated.We compare the crystal qualities and study the relationships between Raman shift and temperature for conventional a-plane GaN epilayer and insertion AlN/AlGaN superlattice layers for a-plane GaN epilayer using temperature-dependent Raman scattering in a temperature range from 83 K to 503 K.The temperature-dependences of GaN phonon modes（A1（TO）,E2（high）,and E1（TO）） and the linewidths of E2（high） phonon peak are studied.The results indicate that there exist two mechanisms between phonon peaks in the whole temperature range,and the relationship can be fitted to the pseudo-Voigt function.From analytic results we find a critical temperature existing in the relationship,which can characterize the anharmonic effects of a-plane GaN in different temperature ranges.In the range of higher temperature,the relationship exhibits an approximately linear behavior,which is consistent with the analyzed results theoretically.

Anti-Stokes/Stokes temperature calibration and its application in laser-heating diamond anvil cells

Anti-Stokes/Stokes Raman peak intensity ratio was used to infer sample temperatures,but the influence factors of system correction factors were not clear.Non-contact in-situ anti-Stokes/Stokes temperature calibration was carried out for up to 1500 K based on six different samples under two excitation light sources(±50 K within 1000 K,±100 K above1000 K),and the system correction factorγwas systematically investigated.The results show that the correction factorγof anti-Stokes/Stokes thermometry is affected by the wavelength of the excitation light source,Raman mode peak position,temperature measurement region and other factors.The anti-Stokes/Stokes thermometry was applied to the laser-heating diamond anvil cell(LHDAC)experiment to investigate the anharmonic effect of h BN under high temperature and high pressure.It is concluded that the strong anharmonic effect caused by phonon scattering at low pressure gradually changes into the predominance of localized molecular lattice thermal expansion at high pressure.

Anharmonic Properties of Aluminum from Direct Free Energy Interpolation Method

We compare the direct free energy interpolation(DFEI) method and the quasi-harmonic approximation(QHA) in calculating of the equation of states and thermodynamic properties of prototype Al. The Gibbs free energy of Al is calculated using the DFEI method based on the high-temperature phonon density of states reduced from classical molecular dynamics simulations. Then, we reproduce the thermal expansion coefficients, the specific heat, the isothermal bulk modulus of Al accurately. By comparing the results from the DFEI method and the QHA, we find that the DFEI method is indeed more accurate in calculating anharmonic properties than the QHA.