Efficient Multi-Configurational Wavefunction Method with Dynamical Correlation Using Non-Orthogonal Configuration Interaction Singles and Doubles (NOCISD)

2019-12-20T07:34:48Z (GMT) by Jacob Nite Carlos A. Jimenez-Hoyos
It is well known that inclusion of dynamical correlation is needed in order to reach quantitative agreement with experiment for molecular systems with multi-reference character. In this work, we start from a non-orthogonal configuration interaction (NOCI) framework that accounts for the static correlation and incorporate dynamical correlation by including singles and doubles excitations out of each reference determinant resulting in a NOCISD wavefunction. The equations defining the NOCISD wavefunction commonly require the solution a poorly condition generalized eigenvalue problem, which we avoid by projecting the equations to a small dimension space defined by the CISD eigenvectors of each reference determinant. We show that NOCISD results are in good qualitative agreement with other state-of-the-art method for challenging problems such as the electron transfer in the ethylene dimer radical cation and LiF, as well as the description of the Jahn-Teller distortion in the cyclopentadienyl and nitrogen trioxide radicals.