ON THE STRUCTURAL-PROPERTIES OF NACL - AN ABINITIO STUDY OF THE B1-B2 PHASE-TRANSITION

The structural properties and the phase transition between the B1 (rock salt) and B2 (CsCl) phases of NaCl have been investigated at an ab initio level. Total energy curves, obtained with periodic Hartree-Fock (HF) calculations, have been corrected a posteriori by integrating the HF charge density according to the correlation-only density-functional-like formulae proposed by Colle and Salvetti (CS75) in 1975 and by Perdew in 1986 (P86) and 1991 (P91). The three functionals are 'non-local', containing terms that depend on the gradient of the electronic density. The correlation correction brings the HF data for the lattice energy (LE), lattice parameter (a(o)) and bulk modulus (B) into good agreement with experiment, the best performance being obtained with the most recent functional, P91 (the percentage error is +0.3%, -0.5% and +5.6% respectively for LE, a(o) and B). The HF transition pressure (39.2GPa) is slightly modified by the CS75 correction (37.2); P86 and P91 functionals reduce the computed value to 30.1 GPa and 28.9 GPa respectively, in better agreement with experiment (30 GPa).