Computer simulation bythe quantum mechanical time-dependent wavepacket method, especiallyfor atom/molecule-solid-surface interaction

Abstract

Thermal energy atomic scattering (TEAS) on solid surfaces formsthe basis of a useful experimental method for obtaining information about the structure, disorder and phonon spectra of the solid surface. Theprobe particles (usually He atoms) can spend a relatively longtime near the solid surface in the interaction region. The dynamicsof the interaction processes cannot be investigated directly atpresent. However, an appropriate physical model of the interactionfitted to the intensity distribution of the scattering may besuitable for use in investigating the interaction processestheoretically, by computer simulation. The present work emphasizesthis computer simulation method. For an actual computersimulation, the detector region TEAS experimental method must be appropriate. Moreover a theoretical model for the TEAS(e.g. a one-particle quantum mechanical wavepacket model governedby the time-dependent Schrödinger equation (TDSE)) and a numericalmethod for solving the TDSE are necessary.The state functions of the consecutive time steps provide enoughinformation to produce an `animation' displaying the dynamics of theinteraction processes. An `animation' is a series of snapshots ofe.g. the probability density function (PDF), taken in rapid succession.The sequence of these snapshots provides a `movie' of the PDF timeevolution.Applications, physical models, numerical solution procedures andsimulation techniques relating to the time-dependentwavepacket (TDWP) method are overviewed in the presentcontribution - especially for the case of TEAS and molecular beamscattering. Several relevant applications of the TDWPmethod - in the case of TEAS - are discussed (to scattering onordered, stepped and adsorbed surfaces, the intensity distributionas a function of transfer width, resonant adsorption and trapping,classical and quantum chaos, scattering from vibrating surfaces).Preliminary results on the quantum chaos in TEAS are presented forthe first time. The theoretical and computational background (theTDWP and coupled channel methods) as well as applications (todiffraction probability, sticking probability, dissociativeadsorption, the steering effect, inelastic channels) ofsix-dimensional molecule/surface dynamics calculations aredescribed.