Phase transitions of deuterated CO(NH2)(2) under pressure

Minimizing the phenomenological potential energy of the deuterated urea we have confirmed the stability of the phase with symmetry: P (4) over bar2(1) m (Z=2), and found two other phases P2(1)2(1)2 (Z=2) and P2(1)2(1)2(1) (Z=4 ), which occur at zero temperature and under increasing pressure. The phase transitions are accompanied by a softening of Gamma (2)(B-1) zone center, and Z(3) zone boundary modes, respectively. (C) 2000 American Institute of Physics. [S0021-9606(00)51942-4].