Orbital optimization:Density matrix-based procedure versus energy minimization

摘要

An iterative method based on the density matrix block diagonalization has recently been proposed.It includes part of the dynamical correlation in the orbital optimization process and provides eithr localized or delocalized symmetry adapted molecular orbitals.The present work compares the so-obtained orbitals with the orbitals given by the traditional energy minimization process.Both analytical derivations and numerical calculations on model systems show that the self-consistent field symmetry-breaking problem is avoided when using the density matrix-based procedure in the case of states presenting a left-right resonance,such as mixed valence compounds or bichromophorice molecules.Accurate calculations of excitation energies in a family of magnetic systems,which generally require highly correlated treatments,can also be obtained at a low computational cost when using these appropriate orbitals.