COMPUTER-SIMULATION OF THE STRUCTURE, SELF-DIFFUSION, AND ELECTRICAL-CONDUCTIVITY OF LIQUID CAF2

Molecular dynamics simulation was used to model liquid (1800, 2000, 22 50, 2500, and 3000 K) and amorphous (T = 0 K) calcium fluoride. The mo del system included 498 ions in a cubic simulation box with periodic b oundary conditions. The Born-Mayer pair potentials contained a single fitting parameter-that for the Ca-F pairs. The simulation runs include d up to 10000 time steps. Structural, thermodynamic, and diffusion pro perties of liquid CaF2 were determined. The calculated energy, density , and compressibility are in reasonable agreement with experimental me asurements. The structure of the amorphous phase is looser than that o f liquid CaF2 at 1800 It. The curves of the mean square displacement o f particles as a function of diffusion time are linear after 8 x 10(-1 2) s. The F- ions diffuse 2 to 3 times faster than the Ca2+ ions. In t he liquid phase, the self-diffusion coefficients rise almost linearly as a function of temperature. The calculated conductivity varies very little in the range 1860-2500 K and is close to experimental values. A t 1800 K virtually no correlation is observed between displacements of Ca+ and F- ions, which are, however strongly correlated in the temper ature range 2500-3000 K.