Reactive scattering using the multiconfiguration time-dependent Hartree approximation: General aspects and application to the collinear H+H2→H2+H reaction

The recently developed multiconfiguration time-dependent Hartree approach (MCTDH) is for the first time applied to quantum reactive scattering. State-resolved reaction probabilities for the collinear H+H2(ν=0,1)→H2(ν=0,1)+H exchange-reaction are calculated and are found to be in excellent agreement with previous results obtained by time-independent methods. To compute the reaction probabilities the initial wavepacket is propagated forward and the final wave packet backwards in time. The Fourier transform at energy E of the time-dependent overlap of both wave packets is then proportional to the S-matrix element. Complex absorbing potentials are shown to be easily implemented in the MCTDH scheme. Fixed single-particle functions are introduced which result in a decrease in computational effort. The MCTDH algorithm requires the potential energy surface to be represented in a particular form. A new scheme for representing potential energy surfaces in a MCTDH adapted form is derived. This scheme can also be used for fitting multidimensional surfaces to given data points.