Considering a mixed atomic basis set composed of only 1s STO and 1s GTO in molecular calculations

Abstract

An atomic basis set composed of only 1s orbitals is introduced, for molecular calculations in the HartreeFock-LCAO approximation. The 1s Slater Type Orbitals are located at the nuclei and the 1s Gaussian Type Orbitals can be used both in fixed locations and as Floating Orbitals. Surprisingly, despite the simplicity of the orbitals, this basis set provides an accurate description of molecular systems containing atoms with two shells such as oxygen and carbon, used as case studies in this work. From a numerical perspective, the basis set is first optimized for the free atoms and then they are introduced into the molecular environment. The molecular calculations for OH_2 and CH_2 show validating results for the energy and the molecular geometry. From the description of the inner atomic and the valence shells achieved with this particular basis set, we can assign a charge to the bonds and the lone pairs by using the Löwdin population analysis, with excellent result from the molecular point of view.