DIRECT CONSTRUCTION OF DIABATIC STATES IN THE CASSCF APPROACH - APPLICATION TO THE CONICAL INTERSECTION OF THE (1)A(2) AND B-1(1) EXCITED-STATES OF OZONE

A generally applicable scheme for the construction of diabatic electronic wavefunctions in the CASSCF/MRCI approach is proposed. It is noted that the redundancy of variational parameters in the CASSCF wavefunction can be exploited to define diabatic molecular orbitals. A maximum-overlap criterion involving orbitals at neighbouring nuclear geometries is employed. In a second step, diabatic N-electron wavefunctions which retain as much as possible their configurational character are constructed by block-diagonalization of the Hamiltonian matrix. The procedure is illustrated by application to the (1)A(2)-B-1(1) conical intersection in ozone.