Unrestricted compact model potentials for ab initio embedded cluster calculations: Magnetic interactions in KNiF3

Abstract

Compact model potentials to introduce the effect of spin-dependent environments in ab initio embedded cluster calculations are reported. The groups forming the environment are described by unrestricted Hartree–Fock wave functions. The method is tested for the magnetic description of KNiF3 by using different model clusters. The cluster calculations are done at the unrestricted Hartree–Fock and unrestricted second-order perturbation levels. The obtained values are in excellent agreement with other more sophisticated ab initio calculations if some Ni–F delocalization is allowed. How the superexchange interaction is accounted for in our method is also discussed.