PRESSURE-DEPENDENCE OF MAGNETIC COUPLING IN IONIC SOLIDS FROM AB-INITIO CLUSTER MODEL-CALCULATIONS

The dependence of the magnetic coupling constant, J, with the pressure has been studied by an ab initio cluster model approach in a typical ionic solid such as KNiF3. By computing J at different values of the lattice parameter R, we predict a power law of the form \J\ approximate to R(-n) with 10.5<n<13.3 in good agreement with the suggested experimental value. This behavior is found even for the simplest Ni2F cluster model described by a complete active space configuration interaction wave function in which the active orbitals correspond to the open shell of each Ni2+ cation.