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Structural phase transitions in Ca2SiO4 and Sr2SiO4 are investigated by molecular dynamics simulations. The simulations are based on the potentials calculated from the Gordon–Kim modified electron gas formalism extended to molecular ions. We successfully reproduced the transition γ -α’H and β-α’L - α’H - α in Ca2SiO4, and the transition β-α’ in Sr2SiO4. We find that the α’L phase of Ca2SiO4 is an ax3b x c superstructure of the α’H phase, while the α’H phase has a β-K2SO4 structure, and the a phase of Ca2SiO4 has a disordered structure with space group P63 /mmc.