The combination of density functional theory with multi-configuration methods - CAS-DFT

CAS-DFT is presented as a method that allows an economical simultaneous tre atment of static and dynamic correlation effects in molecules with multi-re ference character. Central problems of CAS-DFT concern the double counting of dynamic correlation effects and the choice of the proper input quantitie s for the DFT functional. Also, the question of treating both active and in active orbitals in a consistent way is discussed. Test calculations with CA S-DFT for the ring opening of dioxirane and the excitation energies of meth ylene prove that the method works reasonably. (C) 2000 Elsevier Science B.V . All rights reserved.