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Pair-excitationMCSCF treatment of small molecules in an optimized Slater-Transform-Preuss basis set

Güner, Osman F.
Shillady, Donald D.
Ottenbrite, Raphael
Rao, Bhamini K.
Yurtsever, Ersin
Pair‐excitation multiconfigurational self‐consistent field (PEMCSCF) treatment of 11 small molecules (LiH, BeH2, BH3, BF, CH4, C2H4, C2H2, CH2O, NH3, H2O, and HF) has been carried out in a minimum basis set of Slater Transform Preuss functions as fitted by six cartesian gaussians (STP‐6G). The advantages of accuracy without using a split basis are shown by comparison to familiar 4‐31G and 6‐31G calculations using molecular geometries optimized with STO‐6G basis sets. A benefit is shown for the use of minimum basis fitted to STP functions: they overemphasize long‐tail radial dependence to achieve long range basis sensitivity without increasing the basis size at the AO‐to‐MO transformation step in the configuration interaction portion of the MCSCF algorithm. Fully optimized STP‐6G parameters are given and appear to be transferable as shown for acrolein. A FORTRAN listing of the full least squares fitting algorithm is available* for in situ generation of STP‐6G orbitals energetically superior to 4‐31G, or a less accurate STP‐6G 1S, 2S, and 2P basis may be scaled directly as if they were STO‐6G functions, but with considerably lower energy that with an STO‐6G basis.