A Study on atomic populations

Abstract

This study contains theoretical and numerical discussions about the relationship between Mulliken (MAP) and Natural Orbital (NAP) atomic populations. The aim of this analysis is the final use of atomic populations into the atomic shell approximation, where the use of atomic populations instead of atomic numbers, enhances the shape of the approximate first order density functions. The theoretical development shows the algebraic origin of negative AO populations occurrences and proves without doubt the irrelevance of this partial population measure in front of the gross atomic populations. Calculations have been performed on the Cramer steroid family using several basis sets and procedures. Bulk comparisons show some differences when atoms of the same atomic number are compared together. These differences apparently grow as the atomic number increases. However, the comparison of both kinds of atomic populations on the same molecular structure and involving all kinds of atoms produces a high level of matching. One can conclude that MAP and NAP are the same molecular parameters, slightly scaled and shifted from the origin