MRD CI potential surfaces using balanced basis sets. V. Second-row diatomic hydrides

Abstract

Potential energy curves for the ground states of the second-row diatomic hydrides NaH, MgH, …, HCl are calculated using a multireference CI method (MRD CI). The two basis sets used in this paper to obtain the CI energy are the standard double-zeta plus single polarization (DZP) basis, and the same basis set augmented by a set of (s, p) bond functions (BFI basis). Rotation-vibration energy levels derived from these curves are fitted to a spectroscopic expression to obtain ω e, ω eχ 3, ω eω y e and α e. The derived parameters are compared to accurate reference values, and it is shown that the BFI basis gives uniformly better results, including values of D e which are within 0.1 eV of the best estimated experimental values. Freezing the [He] core is shown to be preferable to the [Ne] core for NaH, MgH and AlH. The continued success of BF1 with monohydrides suggests the prescription of BFs based on bond order, independent of a priori calibration. Some calculations are also reported using larger basis sets, including TZPP and BF2, the latter using two sets of (s, p) bond functions to augment the TZPP basis set. In general, the BF basis sets give improved properties relative to the fully nuclear-centered basis sets, and represent an economical way to obtain a compact but accurate starting point for electronic structure calculations.