Simplified box orbitals for molecules containing atoms beyond Ar

Abstract

ABSTRACTSimplified Box Orbitals (SBOs) are a kind of spatially restricted basis functions with a similar use to Slater functions, but fulfilling an exact version of the zero-differential overlap approximation. These functions also allow for a drastic reduction in the number of bielectronic integrals when dealing with huge systems, and can be adapted to study confined systems such as molecules in solution. In previous studies, the necessary SBOs parameters to be used for different elements were defined. However, the accuracy of those basis functions decreases with the atomic number of the atoms under study, and therefore their use was discouraged beyond the Ar atom. In the present study, we verify that slightly increasing the terms of SBOs for a better definition, is enough to correctly handling atoms beyond Ar. This, together with other improvements exposed in this work, allowed obtaining accurate SBOs for K–Kr atoms. To make possible the use of SBOs in standard quantum chemistry calculation software, Gaussian expansions to the proposed basis functions–were achieved. Then, simple formulas for directly obtaining those expansions were deduced. Finally, the results of an SZ basis set of the proposed SBOs are analysed and compared with a similar STO basis set.