First principles calculations on the high-pressure behavior of magnesite

The equation of state and high pressure (>200 GPa) behavior of magnesite we re investigated using first principles pseudopotential calculations based u pon density functional theory within the generalized gradient approximation . Using a third-order Birch-Murnahan equation, the calculations predict a b ulk modulus K-T(0) = 99.0(5) GPa with a partial derivative K/partial deriva tive P = 4.28(1); with a fixed partial derivative K/partial derivative P =4 , the K-T(0) is 111(1) GPa. The results show very good agreement with recen t experimental data. The simulations also confirm experimental studies whic h show that the CO3 groups are rigid incompressible units while the Mg-O bo nd length undergoes significant compression. The fully relaxed calculations show no phase transition within this pressure range, and therefore magnesi te may be stable throughout the lower mantle subject to temperature destabi lization.