Exploring a new time-dependent method for molecular quantum dynamics.

摘要

The electron-nuclear dynamics in chemical processes is described by a method founded on the Time-Dependent Variational Principle (TDVP). In addition, to avoid redundancies in the parametrization of the elecuonic wave function, coherent states (CS) are used. The equations resulting from this treatment enable us to describe the dynamics in general molecular system, since it does not presume a priori knowledge of the potential energy surface of the molecular system. The theory is called Electron Nuclear Dynamics (END).; In order to make this time-dependent method based upon TDVP and CS practical and still realistic, we treat the nuclei in the limit of narrow Gaussian wavepackets (which corresponds to classical nuclei) and use a single determinant to describe the electrons. We name this approach END-SD-FGWP.; We use the END-SD-FGWP approach to study the dynamics of charge transfer in the systems Li{dollar}sp+{dollar}-H--Li {dollar}rightleftharpoons{dollar} Li--H-Li{dollar}sp+{dollar} and Li{dollar}sp+{dollar}-CN-Li {dollar}rightleftharpoons{dollar} Li-CN-Li{dollar}sp+{dollar}. The collision of a proton with H, He, and H{dollar}sb2{dollar} is also investigated by the END-SD-FGWP approach. Several properties of these collisions are compared directly with the experimental results.; Since we are interested in the application of the END formalism to large systems we propose one more approximation, namely, the neglect of the differential diatomic over-lap (NDDO), and introduce the END-SD(NDDO)-FGWP approach. The MNDO/AM1 parametrization is used for the NDDO approach. The computational savings are twofold: (a) the number of integrals computed are reduced by several orders of magnitude compared to the ab initio approach, (b) the equations of motion are simplified, and (c) the high frequency motions of the core electrons is removed by an effective core.