Determination of Accurate Single-Center Expansions with Slater-Type Orbitals: The H3 System

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Abstract
Electronic wavefunctions are determined for the linear symmetric H3 system. The basis functions are Slater‐type orbitals centered on the central proton. For separations of 1.6, 1.7, and 1.8 bohr between adjacent protons, total energies of −1.62648, −1.63074, and −1.62897 a.u. are found using 70‐term configuration‐interaction wavefunctions. These energies are each in error by about 15 kcal/mole. Detailed analysis is made of the convergence. It is concluded that the single‐center Slater‐type orbital basis set is not particularly suited for the simple configuration interaction method for determining many‐electron wavefunctions. It is suggested that higher accuracy might be achieved by using groups of Slater‐type orbitals, taken from off‐center hydrogen‐atom expansions.