Non-orthogonal configuration interaction for the calculation of multielectron excited states.
- Author(s): Sundstrom, Eric J
- Head-Gordon, Martin
- et al.
Published Web Locationhttps://doi.org/10.1063/1.4868120
We apply Non-orthogonal Configuration Interaction (NOCI) to molecular systems where multielectron excitations, in this case double excitations, play a substantial role: the linear polyenes and β-carotene. We demonstrate that NOCI when applied to systems with extended conjugation, provides a qualitatively correct wavefunction at a fraction of the cost of many other multireference treatments. We also present a new extension to this method allowing for purification of higher-order spin states by utilizing Generalized Hartree-Fock Slater determinants and the details for computing ⟨S(2)⟩ for the ground and excited states.