Nonadiabatic effects in two-level systems: A classical analysis

Abstract

International audienceOur aim in this paper is to study classical dynamics in two-level molecular systems. We first derive, through the Wigner phase-space transform, a classical limit that reduces unfortunately to the adiabatic approximation. This lead us to develop a one-center quantal approximation whose variables can be interpreted in a fully classical Hamiltonian scheme. As a prominent feature, this Hamiltonian couples polarization and spatial motion. We apply it successfully to the Rosenthal-Stückelberg oscillations. We analyze one-dimensional diffusion similar to a molecular reaction, it appears to exhibit chaotic behavior

Coupled modes semiclassical treatment of nonadiabatic transitions

“…An improved version of it, known as mean trajectory approximation or hemiquantal treatment, has been proposed [10] where feedback between probability amplitudes and motion of the wavepacket is taken into account. A formalism of that type (called 'one centre approximation'), was used by us to study diffusive chaos in two-level systems [11]. For more complete references and other proposed formalisms see [12].…”

“…The use of Wigner transform [11] and the limith going to zero, leads to the adiabatic approximation. It is not satisfying, as nonadiabatic couplings are lost.…”