A universal basis set for high-precision molecular electronic structure studies

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Abstract
High-precision matrix Hartree-Fock calculations are reported for a series of five isoelectronic diatomic systems in their ground states. A universal even-tempered basis set of Gaussian-type functions is developed for the nitrogen molecule at its experimentally derived equilibrium nuclear separation and then used to parameterize the single-particle state functions in the matrix Hartree-Fock description of the neutral molecules CO and BF, and in the ions NO+ and CN- at their respective experimentally determined equilibrium geometries. The calculated energies are compared with the results of previously reported fully numerical calculations which were performed by using finite difference and/or finite element techniques and which are taken to define Hartree-Fock limit. Energies obtained using the universal even-tempered finite basis set expansion are well within what is usually regarded as 'chemical accuracy' of approximately 1 mHartree and are only in error by approximately 2.3, approximately 1.5, approximately 90, approximately 40 and approximately 140 mu Hartree for N2, CO, BF, NO+ and Cn-, respectively.