Density matrix treatment of localized electronic interactions. Separated electron pairs

Abstract

The density matrix treatment of localized electronic interactions in large systems is extended to separated electron pair wave functions. We make a local space approximation and carry out a Newton–Raphson linearization which leads to effective SCF equations of relatively small dimensionality. Delocalization is included by rigorously satisfying the orthonormality condition on the natural orbitals as well as the normalization requirement on the pair functions. Both the orbitals and the pair coefficients are fully optimized.