Atomistic simulation ofSrF2polymorphs

Abstract

Electron gas interionic potentials (EGIP) have been developed to determine the equation of state (EOS) of the cubic (C1) and orthorhombic (C23) polymorphs of ${\mathrm{SrF}}_{2},$ including the thermal effects by means of a quasiharmonic Debye model. The zero pressure cell parameter ${(a}_{0}),$ lattice energy ${(E}_{\mathrm{latt}}),$ and bulk modulus ${(B}_{0})$ of the C1 phase are computed with errors smaller than 1.2%, 1.2%, and 7.1%, respectively. The predicted EOS is in good agreement with the observed data and satisfies the universal Vinet EOS. For the C23 phase, the optimized zero-$p$ cell parameters a, b, and c and the six fractional coordinates are reported and the pressure dependence of ${a/a}_{0},$ ${b/b}_{0},$ and ${c/c}_{0}$ explored by fitting independent modified Vinet EOS's to the computed data. The analysis reveals a greater compressibility of the C23 phase along the b and c axes than along the a direction. Our calculation predicts the $\mathrm{C}1\ensuremath{\rightleftharpoons}\mathrm{C}23$ equilibrium to occur at ${p}_{\mathrm{tr}}=3.92$ GPa, which is between the observed values for the $\mathrm{C}\stackrel{\ensuremath{\rightarrow}}{1}\mathrm{C}23$ ${(p}_{\mathrm{tr}}=5.0$ GPa) and $\mathrm{C}23\ensuremath{\rightarrow}\mathrm{C}1$ ${(p}_{\mathrm{tr}}=1.7$ GPa) phase transitions.