Unitary Optimization of Localized Molecular Orbitals.

A unified formalism and its implementation is presented for Foster-Boys, fourth moment, Pipek-Mezey, and Edmiston-Ruedenberg type localization schemes of molecular orbitals through unitary optimization of the localizing transform matrix using a recently proposed algorithm [ Abrudan ; et al. Signal Processing 2009 , 89 , 1704 ]. A conjugate gradient algorithm is used with an efficient line search method. The option of using complex valued orbitals is included. Applications to fullerenes from C20 to C100, as well as benzene and arachic acid are presented, showing the capability of the method, which has been implemented in ERKALE, an open source program for electronic structure calculations of atoms and molecules.