Extension of density functional theory to nuclear orbital plus molecular orbital theory: Self-consistent field calculations with the collesalvetti electronnucleus correlation functional

Non BornOppenheimer self-consistent field calculations including not only electronelectron (ee) exchange correlation but also electronnucleus (en) correlation energies have been carried out. In this study, ColleSalvetti and B3LYP functionals for the en correlation and ee exchange-correlation energies are adopted. Numerical assessments confirm that the standard enthalpies of formation are well reproduced for the G2-1 set. We also apply this method to ammoniated ammonium ion (N₂H₇⁺), one of the "vibrational bonding" systems, and discuss nuclear quantum effects such as the isotope effect.