Analysis of optical absorption spectra of transition metal cluster ions by the spin-polarized DV- Xα method

Abstract

Optical absorption spectra of cobalt cluster ions, Con+, and vanadium cluster ions, Vn+, were analyzed by a theoretical calculation based on the spin-polarized DV-Xα method, and their electronic and geometric structures were obtained. Relative absorption cross section associated with each electronic transition was calculated; the calculation enables a qualitative comparison of calculated spectrum with a measured one not only in its transition energy but also in its intensity profile. This analysis shows that Co4+, Co3+, and V4+ have, respectively, a tetrahedral structure with a bond distance of 2.00A, an equilateral triangle with a bond distance of 2.30A, and a distorted tetrahedral structure with five bonds having a distance of 2.34 A and one of 2.89A. The differences in the population between majority and minority spins (spin-difference) evaluated from the electronic structure thus obtained were 2.0, 1.7, and zero per atom in Co3+, Co4+, and V4+, respectively. These spin differences indicate a ferromagnetic and an antiferromagnetic spin-coupling in the cobalt and vanadium cluster ions, respectively.