Non-Born–Oppenheimer molecular wave functions of H2 by extended multi-configuration time-dependent Hartree–Fock method

A ground state wave function of a one-dimensional H2 molecule is derived numerically by the extended multi-configuration time-dependent Hartree–Fock (MCTDHF) method. The electronic orbitals and the amplitudes for the nuclear motion constituting the ground-state wave function are derived by solving the coupled equations of motion by the imaginary time propagation. Comparisons with the results obtained by the Born–Huang (BH) expansion method as well as with the exact wave function reveal that the memory size required in the extended MCTDHF method is about two orders of magnitude smaller than in the BH expansion method.