Numerical coupled Liouville approach: Quantum dynamics of linear molecular aggregates under intense electric fields

摘要

We develop a numerical calculation scheme of a dynamics of the quantum network for linear molecular aggregates under time-dependent electric fields. Each molecule is assumed to be an electric dipole arranged linearly with an arbitrary angle from the longitudinal axis. This approximation is considered to be appropriate for the aggregates with large intermolecular distances and allows us to treat intermediate- and large-size aggregates without enormous direct calculations of the Coulomb interactions. The molecular interactions are taken into account by adding the radiations from these dipoles to the external electric fields. The dynamics is performed by solving the coupled Liouville equation constructed from the Liouville equation for each dipole. The effects of the retarded electric fields are evaluated with numerically exact precision by using the sixth-order Runge-Kutta scheme. As a simple example, we examine the linear aggregates involving two dipoles composed of two-state molecules under the continuous laser fields. The effects of the intensity of external fields, the intermolecular distances, and the angles between the dipole and the longitudinal axis on the population differences are investigated. The linear polarizability spectra are calculated by using the definition of nonperturbative polarizability. An abrupt change like the phase-transition behavior in the variation in the population differences for the applied field intensities is observed for the dimer models. Based on these results, we anticipate the population differences for larger (intermediate)-size aggregates. (C) 1998 John Wiley & Sons, Inc. [References: 9]