Jk. Dewhurst et al., HIGH-PRESSURE PHASES OF SIO2 USING LOCAL-DENSITY AND GENERALIZED-GRADIENT APPROXIMATIONS, Physical review. B, Condensed matter, 55(17), 1997, pp. 11003-11005
Plane-wave calculations using the local-density approximation (LDA) ar
e compared with those using the generalized-gradient approximation (GG
A) in various high-pressure polymorphs of silica. The GGA gives lower
cohesive energies and bulk modulii than the LDA but larger equilibrium
unit-cell volumes. The cellular structure of the high-pressure post-s
tishovite (CaCl2) phase is examined and suggested having a slightly la
rger bulk modulus than stishovite. Trends in properties of the various
phases are nearly similar using both approaches.