Density functional calculations of the structure of crystalline urea underhigh pressure

The geometry of the urea crystal is optimized for several different pressur es using a pseudopotential density functional (DFT) approach with a plane-w ave basis set and the Ceperley-Alder local density correlation potential. A ll the optimized intra- and intermolecular geometrical parameters, as well as the lattice vectors, are found to be in good agreement with experiment. Under high pressures, the crystal changes anisotropically; the lattice cons tants a and b reduce by almost 10 times mole with the pressure than the con stant c. Changes of the geometrical parameters within the molecule as a fun ction of the external pressure are found to be in good agreement with the d onor-acceptor theory. (C) 2000 Elsevier Science B.V. All rights reserved.