Atomistic simulation of SrF2 polymorphs -: art. no. 094107

Electron gas interionic potentials (EGIP) have been developed to determine the equation of state (EOS) of the cubic (C1) and orthorhombic (C23) polymorphs of SrF2, including the thermal effects by means of a quasiharmonic Debye model. The zero pressure cell parameter (a(0)), lattice energy (E-laft), 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 C1=C23 equilibrium to occur at p(tr)=3.92 GPa, which is between the observed values for the C1-->C23 (p(tr)= 5.0 GPa) and C23-->C1 (p(tr)= 1.7 GPa) phase transitions.