Geometry optimization within a localized CAS-SCF approach

A CAS-SCF algorithm based on molecular orbitals that conserve their physical nature during the iterative process has been recently proposed. The algorithm is based on the iterative partial diagonalization of the one-body density matrix obtained from a SuperCI-like procedure. If localized guess orbitals are used, the locality property is conserved by the final orbitals, and the algorithm is particularly suitable for the study of local processes (e.g., bond breaking) in large molecules. In this work, it is shown that the localized orbitals obtained in such a way can be supplied to a standard CAS-SCF geometry-optimization package, in order to find the optimal geometry relaxation with a given local active space. The procedure is illustrated in the case of the rotation of the CH2 group around the CC double bond in the acroleine molecule.