Molecular dynamics simulation of high-pressure clinoenstatite

A high pressure polymorph of clinoenstatite (HP-CEn) was studied using molecular dynamics (MD) simulations, based on empirical potential parameters. Starting from the MD-simulated structure of high-temperature clinoenstatite (HT-CEn) at 2000K and 0GPa, the subsequent MD calculations were carried out by increasing pressures up to 18GPa at intervals of 3GPa. Above 15GPa the MD-simulated crystals are HP-CEn characterized by their notably small β angles (99-100 degrees). Structure factors calculated from the resulting atomic positions reveal that the MD-simulated HP-CEn has a C2/c symmetry in common with the HT-CEn. The discontinuous change of the MD-simulated cell parameters with conspicuous hystereses between HT-CEn and HP-CEn, which implies a first-order phase transition, was first found in the present paper and suggests that the two clinoenstatites belonging to the same space group are two separated phases with large and small angles of the chain extension.