Iterative diagonalization within the multi-configurational time-dependent Hartree approach: calculation of vibrationally excited states and reaction rates

An iterative diagonalization scheme for operators involving wavepacket propagations employing the multi-configurational time-dependent Hartree (MCTDH) approach is presented. The scheme is based on a Lanczos-type recursion relation, which is modified to account for the different sets of single-particle functions employed in different MCTDH wavefunctions. Two possible applications are given: the calculation of energies and eigenfunctions of vibrationally excited states, and the direct calculation of thermal rate constants. The electronic ground state of CH3I including four vibrational coordinates and the collinear H + H2 reaction have been used as testing examples.