Electron density in RbBr and CsI crystals in the self-consistent local-density-functional approximation (LDA)

Abstract

The electron density in RbBr and CsI crystals - composed of 'isoelectronic' alkali and halogen ions - has been computed self-consistently by the method of augmented spherical waves in the LDA approximation. The heat of formation of the salts from the alkali metal and the halogen molecule - calculated from the pertinent total energies - is in very good agreement with experiment. The LDA structure factors for the low-order 'sum' and 'difference' reflections are compared with the structure factors obtained from Hartree-Fock free-ion wave functions. The agreement is excellent for the 'sum' reflections, but for the 'difference' reflections the LDA structure factors are smaller. This result parallels our earlier results for NaF and KCI crystals and again indicates a 'contraction' of the anion and an 'expansion' of the cation in passing from free ion to ion in crystal.