Unconventional bond functions for quantum chemical calculations

Mester, Dávid and Csontos, József and Kállay, Mihály (2015) Unconventional bond functions for quantum chemical calculations. THEORETICAL CHEMISTRY ACCOUNTS, 134 (6). No. 74. ISSN 1432-881X

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Abstract

New types of bond function (BF) basis sets are proposed and tested for quantum chemical applications. First, BF basis sets constituted of conventional Gaussiantype orbitals (GTO) are considered. Both the exponents and the positions of the BFs are optimized, but, in contrast to previous studies, the position of each BF shell is varied separately. Second, new types of basis functions, the general ellipsoidal Gaussian-type orbitals (EGTOs), are proposed for quantum chemical applications. The EGTOs are distorted spherical GTOs and, as such, are expected to be well suited for describing the polarized charge densities in molecular environments. EGTOs can be used either as atom-centered (AC) basis functions or as BFs. In this study, the latter possibility is explored, and BF basis sets including EGTOs are optimized and compared to those containing only conventional GTO BFs. The performance of the developed GTO and EGTO BF basis sets is assessed for Hartree-Fock and density functional calculations against conventional AC GTO basis sets. Our results show that using GTO BF basis sets, the results are significantly improved, while the number of the basis functions can be decreased by about 10 %, which is not dramatic; however, the average angular momentum quantum number in the BF sets is significantly lower. The accuracy of the computed energies can be further increased by about 15 % if EGTO BFs are used.

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