Pair-excitation MCSCF treatment of small molecules in an optimized Slater–Transform–Preuss basis set

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.