No abstract

Despite its promise as a method for the simulation of time-dependent many-body quantum mechanics problems, wave packet molecular dynamics (WPMD) is limited in its use by wave packet spreading when applied to dense plasma systems. We employ more accurate methods to determine if spreading really occurs and how WPMD can be improved. A scattering process involving a single dynamic electron interacting with a periodic array of statically screened protons is used as a model problem for the comparison. We compare the numerically exact split operator Fourier transform (SOFT) method, the Wigner trajectory method (WTM), and the time dependent variational principle (TDVP). Within the framework of the TDVP, we use the standard variational form of WPMD, the single Gaussian wave packet (WP). We then generalize this form to include multiple Gaussian for the single electron as in the split WP propagation method. Wave packet spreading is predicted by all methods, so it is not the source of the unphysical behavior of WPMD at high temperatures.Instead, the Gaussian WP's inability to correctly reproduce breakup of the electron's probability density into localized density near the protons is responsible for the deviation from more accurate predictions. Extensions of WPMD must include a mechanism for breakup to occur in order to yield dynamics that lead to accurate electron densities.

We present here a detailed analysis of the mechanism of photoinduced electron and proton transfer in the planar pyrrole-pyridine hydrogen-bonded system, a model for the photochemistry of hydrogen bonds in DNA base pairs. Two different crossings, an avoided crossing and a conical intersection, are the key steps for forward and backward electron and proton transfer providing to the system photostability against UV radiation by restoring the system in its initial electronic and geometric structure.