A fast intrinsic localization procedure applicable forabinitioand semiempirical linear combination of atomic orbital wave functions

摘要

A new intrinsic localization algorithm is suggested based on a recently developed mathematical measure of localization. No external criteria are used to defineaprioribonds, lone pairs, and core orbitals. It is shown that the method similarly to Edmistonndash;Ruedenbergrsquo;s localization prefers the well established chemical concept of sgr;ndash;pgr; separation, while on the other hand, works as economically as Boysrsquo; procedure. For the application of the new localization algorithm, no additional quantities are to be calculated, the knowledge of atomic overlap intergrals is sufficient. This feature allows a unique formulation of the theory, adaptable for bothabinitioand semiempirical methods, even in those cases where the exact form of the atomic basis functions is not defined (like in the EHT and PPP calculations). The implementation of the procedure in already existing program systems is particularly easy. For illustrative examples, we compare the Edmistonndash;Ruedenberg and Boys localized orbitals with those calculated by the method suggested here, within both the CNDO/2 andabinitioframeworks (using STOhyphen;3G and 6hyphen;31Gast;ast; basis sets) for several molecules (CO, H2CO, B2H6, and N2O4). Some similarities concerning the localization procedures of von Niessen as well as Magnasco and Perico are also discussed.