The conditions for optimal reflection-free complex-absorbing potentials (CAPs) are discussed. It is shown that the CAPs as derived from the smooth-exterior-scaling transformation of the Hamiltonian, [J. Phys. B. 31, 1431Phys. B. 31, (1998], serve as optimal reflection-free CAPs (RF-CAPs) in wave-packet propagation calculations of open systems. The initial wave packet, Φ(t = 0) can be located in the interaction region (as in half collision experiments) where the CAPs have vanished or in the asymptote where VCAP = 0. As we show the optimal CAPs can be introduced also in the region where the physical potential has not vanished. The un-avoided reflections due to the use of a finite number of grid points (or basis functions) are discussed. A simple way to reduce the "edge-grid" reflection effect is described.
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Effects of anharmonic bridge vibrations on electronic tunneling in donor-bridge-acceptor complexes are studied using a model of anharmonic bridge vibration coupled nonlinearly to an electronic degree of freedom. An anharmonicity parameter is introduced, enabling to reproduce the standard harmonic model with linear coupling as a limiting case. The frequency of electronic tunneling oscillations between the donor and acceptor sites is shown to be sensitive to the nuclear anharmonicity, where stretching and compression modes have an opposite effect on the electronic frequency. This phenomenon, that cannot be accounted for within the harmonic approximation, is analyzed and explained.
Possible mechanisms for charge-transport-induced dissociation in donor-bridge-acceptor complexes are studied. Two mechanisms for dissociation at the molecular bridge are captured within a simple model of an anharmonic bridge vibration coupled nonlinearly to an electronic degree of freedom. A direct mechanism is associated with vibronic excitations to the nuclear continuum and an alternative dissociation mechanism involves intermediate quasibound vibrational states (Feshbach resonances). The two different mechanisms of charge-transport-induced dissociation are analyzed and their interplay as a function of the system parameters is examined. A parameter regime is suggested where the phenomenon should be experimentally accessible.
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