Development of the explicitly correlated Gaussian–nuclear orbital plus molecular orbital theory: Incorporation of electron–electron correlation

This Letter proposes a scheme to incorporate electron–electron (e–e) correlation for the explicitly correlated Gaussian–nuclear orbital plus molecular orbital (ECG–NOMO) theory, which offers accurate descriptions for electronic and nuclear states. The second order Møller–Plesset perturbation theory and coupled-cluster theory with singles and doubles in the ECG–NOMO framework are adopted for evaluating the e–e correlation. Illustrative applications for dihydrogen, trihydrogen cation molecules, and their isotopomers confirm significant improvement for the total energies and zero-point energies.