On the inclusion of dissipation on top of mean-field approaches
Dinh PM, Lacombe L, Reinhard PG, Suraud E, Vincendon M (2018)
Publication Type: Journal article
Publication year: 2018
Journal
Book Volume: 91
Article Number: 246
Journal Issue: 10
DOI: 10.1140/epjb/e2018-90147-0
Abstract
We discuss extensions of time-dependent mean-field theories such as time-dependent local density approximation (TDLDA) in order to include incoherent dynamical correlations, which are known to play a key role in far-off equilibrium dynamics. We focus here on the case of irradiation dynamics in clusters and molecules. The field, still largely unexplored, requires quantum approaches which represents a major formal and computational effort. We present several approaches we have investigated to address such an issue. We start with time-dependent current-density functional theory (TDCDFT), known to provide damping in the linear regime and explore its capability far-off equilibrium. We observe difficulties with the scaling of relaxation times with deposited energy. We next briefly discuss semi-classical approaches which deliver kinetic equations applicable at sufficiently large excitation energies. We then consider a first quantum kinetic equation at the level of a simplified, though rather elaborate in its content, relaxation time approximation (RTA). Thanks to its sophistication, the method allows us to address numerous realistic irradiation scenarios beyond the usual domain of reliability of such theories. We demonstrate in particular the key role played by dense spectral regions in the impact of dissipation in the response of the irradiated system. RTA nevertheless remains a phenomenological approach which calls for more fundamental descriptions. This is achieved by a stochastic extension of mean field theory, coined stochastic time dependent Hartree–Fock (STDHF), which provides an ensemble description of far-off equilibrium dynamics. The method is equivalent to a quantum kinetic equation complemented by a stochastic collision term. STDHF clearly leads to proper thermalization behaviors in 1D test systems considered here. It remains limited by its ensemble nature which requires possibly huge ensembles to properly sample small transition rates. An alternative approach, coined average STDHF (ASTDHF), consists in overlooking mean field fluctuations of STDHF. ASTDHF provides a robust tool, properly matching STDHF when possible and allowing extension to realistic dynamical scenarios in full 3D. It can also be used in open systems to explore, as done in RTA, the competition between ionization and dissipation.
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APA:
Dinh, P.M., Lacombe, L., Reinhard, P.-G., Suraud, E., & Vincendon, M. (2018). On the inclusion of dissipation on top of mean-field approaches. European Physical Journal B, 91(10). https://doi.org/10.1140/epjb/e2018-90147-0
MLA:
Dinh, Phuong Mai, et al. "On the inclusion of dissipation on top of mean-field approaches." European Physical Journal B 91.10 (2018).
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