First-principles study of lattice dynamics and thermodynamics of osmium under pressure

Abstract

We have performed the first-principles linear response calculations of the lattice dynamics, thermal equation of state and thermodynamical properties of hcp Os metal by using the plane-wave pseudopotential method. The thermodynamical properties are deduced from the calculated Helmholtz free energy by taking into account the electronic contribution and lattice vibrational contribution. The phonon frequencies at Gamma point are consistent with experimental values and the dispersion curves at various pressures have been determined. The calculated volume, bulk modulus and their pressure derivatives as a function of temperature are in excellent agreement with the experimental results. The calculated specific heat indicates that the electronic contribution is important not only at very low temperatures but also at high temperatures due to the electronic thermal excitation. The calculated Debye temperature at a very low temperature is in good agreement with experimental values and drops to a constant until 100 K.

Modification of Lu's (2005) high pressure model for improved high pressure/high temperature extrapolations. Part II: Modeling of osmium–platinum system at high pressure/high temperature

“…Osmium has been the subject of numerous DFT calculation studies [21,25,[37][38][39][40][41][42][43][44][45][46] using different techniques and approximations (see Table 2). Our own calculations will be presented in the next section.…”

“…[44] was also selected. This author was chosen in preference to others giving the same type of calculation [40][41][42][43] because it reproduces reasonably well the thermal expansion at ambient pressure and because it has intermediate values between the other authors. This data together with the high temperature compressibility [32] allowed to assess the cut-off pressure in the model (parameter ).…”

Ab initio study of the density dependence of the Grϋneisen parameter at pressures up to 360 GPa

“…Hence our studies are limited to platinum, palladium, rhodium, and iridium at temperatures up to 2000K. In both the cases the basic criterion for the choice of a system for study was the stability of its crystal structure over the entire range of thermodynamic conditions studied [35][36][37][38][39][40][41][42][43][44][45][46][47][48][49]. The basic results of our studies are the following: (i) We show that the ratio of the density over either ϒ vib (at zero temperature) or ϒ th (at a fixed non-zero temperature) is a linear function of density to a very good approximation over a large and useful range of densities (corresponding to pressures up to 360 GPa -approximately the pressure at the Earth's core).…”

Calculated Hyperfine Coupling Constants And Geometric Parameters For 3,3,5,5-Tetramethylpyrroline-N-Oxide Radical Products With EPR Spin Trapping

“…The correlation of radical structure with spin adducts parameters had studied by Lawrence and et al [7]. The hyperfine parameters of some radicals were studied by using the density function theory (DFT) and configuration-interaction (CI) methods [8]. Some authors have calculated the g-tensors of some organic radicals by Hartreee Fock (HF) method [9].…”