A method to calculate the weights of nbo electronic structures from Moffitt's theorem

Abstract

A method is presented allowing the calculation of the weights of Natural Bond Orbital (NBO) electronic structures, providing the probabilities to find simultaneously electrons and electron pairs in various types of bond orbitals. The MO wave function is assumed to be known, and can be of any type (e.g., uncorrelated or correlated). The used transformation process of the initial MO wave function and Moffitt's theorem are combined so that the calculation of the weights does not involve any approximation. The method is general, holding for any system and for any type of NBOs, but the chemical interpretation is more conveniant for systems having one dominant Lewis structure. The methylamine molecule in minimal, double zeta, and double zeta plus polarization basis sets is considered as an example to illustrate the method. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 306–315, 2001