Density matrix method for orbital localization.

A method is presented for localizing molecular orbitals, based on diagonalizing subunits of the density matrix. First, nonbonding orbitals are found by diagonalizing the monatomic subunits; then, diatomic sigma or pi bonding and antibonding orbitals are obtained from the diatomic subunits for all bonded pairs of atoms; finally, the delocalized pi-orbitals for particular chromophores are found by projecting the first set out of the self-consistent field (SCF) Hamiltonian. The results show good general agreement with other localization methods, with advantages in the ability to display group orbitals in complex molecules which most closely resemble the SCF orbitals for simple prototypes.