The spin density and the optical spectrum of CoCl^2-₄

Abstract

The CoCl^2- ₄ ion has been studied using ab initio methods at various levels of approximation (RHF, UHF, CI and MC SCF). The calculations have been performed both with and without the Madelung field from crystalline surroundings. One of the main purposes has been to investigate the spin density, and determine its dependence on both correlation and external fields. The spin density is found to be fairly dependent on correlation but rather independent of the surrounding crystal. The lower excited quartet states have been calculated using CI expansions based upon ground state RHF and MC SCF wavefunctions. The experimental spectrum is very well reproduced on the MC SCF/CI level, both with and without the Madelung field.