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Published December 14, 2012 | Published
Journal Article Open

Consistent schemes for non-adiabatic dynamics derived from partial linearized density matrix propagation

Abstract

Powerful approximate methods for propagating the density matrix of complex systems that are conveniently described in terms of electronic subsystem states and nuclear degrees of freedom have recently been developed that involve linearizing the density matrix propagator in the difference between the forward and backward paths of the nuclear degrees of freedom while keeping the interference effects between the different forward and backward paths of the electronic subsystem described in terms of the mapping Hamiltonian formalism and semi-classical mechanics. Here we demonstrate that different approaches to developing the linearized approximation to the density matrix propagator can yield a mean-field like approximate propagator in which the nuclear variables evolve classically subject to Ehrenfest-like forces that involve an average over quantum subsystem states, and by adopting an alternative approach to linearizing we obtain an algorithm that involves classical like nuclear dynamics influenced by a quantum subsystem state dependent force reminiscent of trajectory surface hopping methods. We show how these different short time approximations can be implemented iteratively to achieve accurate, stable long time propagation and explore their implementation in different representations. The merits of the different approximate quantum dynamics methods that are thus consistently derived from the density matrix propagator starting point and different partial linearization approximations are explored in various model system studies of multi-state scattering problems and dissipative non-adiabatic relaxation in condensed phase environments that demonstrate the capabilities of these different types of approximations for treating non-adiabatic electronic relaxation, bifurcation of nuclear distributions, and the passage from nonequilibrium coherent dynamics at short times to long time thermal equilibration in the presence of a model dissipative environment.

Additional Information

© 2013 American Institute of Physics. Received 4 June 2012; accepted 14 August 2012; published online 4 September 2012. We gratefully acknowledge support for this research from the National Science Foundation (NSF) under Grant No. CHE-0911635 and support from Science Foundation Ireland under Grant No 10/IN.1/I3033. D.F.C. acknowledges the support of his Stokes Professorship in Nanobiophysics from Science Foundation Ireland. We also acknowledge a grant of supercomputer time from Boston University's Office of Information Technology and Scientific Computing and Visualization. Finally, we would like to thank John Tully for inspiring our work in this area.

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August 22, 2023
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