DERIVATION OF ELECTRON-GAS INTERATOMIC POTENTIALS FROM QUANTUM-MECHANICAL DESCRIPTIONS OF IONS IN CRYSTALS

The electron-gas-model theory is critically examined by means of interatomic potentials developed from ab initio quantum-mechanical descriptions of ions embedded in a crystalline environment and from the basic hypotheses of the model, namely, spherically symmetric and additive ionic electron densities, plus energy functionals for a homogeneous electron gas. We have found that the quantum-mechanical crystal potential enhances the deformation of the ionic wave functions induced by the crystal formation with respect to the self-consistent, crystal-adapted densities previously used in electron-gas simulations. Since these differences are dependent on the crystal strain, it is shown that some of the good results obtained in earlier electron-gas-based computations may be partially due to a cancellation effect between the assumptions of the model and the approximate description of the constitutive ions. For the test case explored here, the NaCl equation of state and the B1-B2 pressure-induced phase transition, the overall agreement with the experimental data is recovered when the electronic densities and the energetic interactions are both computed quantum mechanically. © 1995 The American Physical Society.