Ab initio elasticity and thermal equation of state of MgSiO3 perovskite

We have used high-temperature ab initio molecular dynamic simulations to st udy the equation of state of orthorhombic MgSiO3 perovskite under lower man tle pressure-temperature conditions. We have determined the Gruneisen param eter, gamma, as a function of volume. Our state-of-the-art simulations, acc urate to within 10%, resolve the long-standing controversy on thermal expan sion (a) and Gruneisen parameter of MgSiO3 perovskite. Under ambient condit ions we find the values for alpha and gamma of 1.86 x 10(-5) K-1 and 1.51, respectively, in excellent agreement with the latest experimental studies. Calculated elastic constants and the static equation of state at 0 K agree well with previous simulations. We have found no evidence for the high-temp erature phase transitions of orthorhombic MgSiO3 perovskite to cubic or tet ragonal phases at mantle temperatures. (C) 2001 Elsevier Science B.V. All r ights reserved.