Analyzing molecular static linear response properties with perturbed localized orbitals

Perturbed localized molecular orbitals (LMOs), correct to first order in an applied static perturbation and consistent with a chosen localization functional, are calculated using analytic derivative techniques. The formalism is outlined for a general static perturbation and variational localization functionals. Iterative and (formally) single-step approaches are compared. The implementation employs an iterative sequence of 2 X 2 orbital rotations. The procedure is verified by calculations of molecular electric-field perturbations. Boys LMO contributions to the electronic static polarizability and the electric-field perturbation of the < r(2)> expectation value are calculated and analyzed for ethene, ethyne, and fluoroethene (H2C=CHF). For ethene, a comparison is made with results from a Pipek-Mezey localization. The calculations show that a chemically intuitive decomposition of the calculated properties is possible with the help of the LMO contributions and that the polarizability contributions in similar molecules are approximately transferable. (C) 2010 American Institute of Physics. [doi:10.106311.3455709]