Isopycnic orbital transformations and localization of natural orbitals

Abstract

Properties of linear orbital transformations that leave the first-order density matrix invariant are investigated. These isopycnic orbital transformations make possible to localize not only the Hartree-Fock spin-orbitals, but the natural spin-orbitals, as well. A new localization procedure, based on atomic overlap matrices, is proposed to facilitate interpretation of the localized natural spin-orbitals (LNOS). Changes in LNOS upon breaking of a single bond in the H2 and HF molecules are examined. The LNOS are also computed for the CO and LiF molecules and compared with the localized molecular orbitals.