Electronic transition dipole moments from orthogonality constrained Hartree–Fock wavefunctions

In our recent paper (Glushkov V N and Assfeld X 2016 Theor. Chem. Acc. 135), we have presented some applications of the so-called orthogonality constrained Hartree–Fock (OCHF) theory to calculations of excited state energies of the same symmetry, including highly and core excited states. In this paper we report an attempt to apply this methodology to practical calculations of electronic dipole transition moments focusing on transitions between states having the same spatial symmetry as the ground state. Basic tenets of this method are briefly reviewed and its specific features for ab initio calculations of electronic transitions are discussed. The effect of non-orthogonal HF wave functions on transition dipole moments is studied and analyzed. OCHF electronic transition moments calculated for the HeH molecule are presented as a function of the internuclear separation for five ²Σ⁺ states ( X ²Σ⁺, A ²Σ⁺, C ²Σ⁺, D ²Σ⁺and F ²Σ⁺). The results of the calculations are, in general, in good agreement with those obtained by multi-reference configuration interaction methods which take correlation effects into account and show a favorable balance between accuracy and computational efficiency. (paper)