Multiconfigurational nuclear-electronic orbital approach: Incorporation of nuclear quantum effects in electronic structure calculations

The nuclear-electronic orbital (NEO) method for the calculation of mixed nuclear-electronic wave functions was presented. The electronic and nuclear molecular orbitals were expressed as linear combinations of Gaussian basis functions. In the NEO-configuration interaction (CI) method, the energy corresponding to the multiconfigurational mixed nuclear-electronic wave function was minimized with respect to the CI coefficients. Analytic gradient expressions were presented for NEO-Hartree-Fock (HF) and NEO-multiconfigurational self-consistent-field.