ASNCA3 AT HIGH-PRESSURE

A constant pressure optimization scheme is applied to the study of ter nary calcium nitrides under pressure, The enthalpy is minimized with r espect to the electronic configuration, the positions of the atoms and the cell metric (i,e, the lattice parameters). Symmetry corrections c an be performed during the relaxation towards the equilibrium structur e in order to be able to investigate the compound in a certain propose d symmetry. We obtain excellent agreement with experiment for the zero -pressure structural parameters of the cubic anti-perovskite structure BiNCa3 and of the distorted anti-perovskite structures AsNCa3 and PNC a3. For AsNCa3 the structural parameters, band gap energies, etc. an i nvestigated as a function of the pressure. A new cubic phase is predic ted to have a lower enthalpy than the orthorhombic phase for pressures above 59 GPa. Copyright (C) 1998 Elsevier Science B.V.