On the integration of the multi-configurational time-dependent Hartree (MCTDH) equations of motion

The multi-configurational time-dependent Hartree approach facilitates multi-dimensional wave packet calculations studying polyatomic reaction processes. The efficiency of the approach results from the use of an optimally adapted time-dependent basis of single-particle functions employed in the wavefunction representation. As a consequence, the equations of motion are non-linear. An efficient integration scheme for these equations has been developed by Beck and Meyer [Z. Phys. D 42 (1997) 113]. The scheme is optimally suited for studies of systems where the Hamiltonian can be represented as a sum of products of single-particle operators. Employing the same basic ideas, the present work now introduces and discusses revised integration schemes which are more efficient for systems, where the Hamiltonian includes a general potential energy function. The H + CH4 → H2 + CH3 reaction is employed as an example to test the efficiency of the different schemes.