The multiconfiguration time‐dependent Hartree–Fock method based on a closed‐shell‐type multiconfiguration self−consistent field reference state and its application to the LiH molecule

The linear response calculations in the multiconfiguration time‐dependent Hartree–Fock (MCTDHF) approximation with a closed‐shell‐type MCSCF state as the time‐independent reference state are discussed. The application to the LiH molecule with a small basis set ([4s2p1d/2s1p]) shows validity of our MCTDHF approach to the singlet ground state. Our MCSCF correlation energy is 97% of the total (=full CI) correlation energy and the MCTDHF excitation energies are in good agreements with the Δ full CI excitation energies. The Born–Oppenheimer potential energy curves for the lowest three singlet states of LiH and the corresponding vibrational level spacings, the transition moments, the oscillator strengths, and the frequency‐dependent dipole polarizabilities are reported. All of these results imply the potentiality of our MCTDHF method for the future work with the larger basis set. One of such basis sets ([9s8p4d/8s7p1d]) is referentially used only at the single‐configuration TDHF level, and the resultant near‐Hartree–Fock polarizability and Thomas–Reiche–Kuhn sum rule is very promising.