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) polymo rphs of SrF2, including the thermal effects by means of a quasiharmonic Deb ye 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 th an 1.2%, 1.2%, and 7.1%, respectively. The predicted EOS is in good agreeme nt with the observed data and satisfies the universal Vinet EOS. For the C2 3 phase, the optimized zero-p cell parameters a, b, and c and the six fract ional 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 c omputed data. The analysis reveals a greater compressibility of the C23 pha se along the b and c axes than along the a direction. Our calculation predi cts 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.