Ab initio calculations of effective exchange integrals for triplet carbene clusters. Importance of stacking modes for ferromagnetic interactions

Abstract

An ab initio method is presented to calculate the effective exchange integrals ( J ab ) for exchange-coupled clusters on the basis of the approximately projected UHF (APUHF) and UHF Møller-Plesset (APUMP) procedures. The APUMP method is applied to the calculation of the effective exchange integrals for clusters of triplet carbenes in order to elucidate variations of J ab values with the basis set and correlation corrections. The signs and magnitudes of the J ab values calculated for clusters of phenyl carbenes by the APUHF STO-3G method are found to be compatible with the observed data, indicating the importance of stacking modes for ferromagnetic interactions.