Eur. Phys. J. B 77, 305-329 (2010)
https://doi.org/10.1140/epjb/e2010-00280-5

Modelling non-adiabatic processes using correlated electron-ion dynamics

¹ Interdisciplinary Centre for Advanced Materials Simulation, Ruhr-Universität Bochum, Stiepeler Strasse 129, 44801 Bochum, Germany
² Department of Chemistry, Tulane University, New Orleans, Louisiana, 70118, USA
³ Atomistic Simulation Centre, School of Mathematics and Physics, Queen's University of Belfast, Belfast, BT7 1NN, UK
⁴ Nano-Bio Spectroscopy Group and ETSF Scientific Development Centre, Dpto. Física de Materiales, Universidad del País Vasco, Centro de Física de Materiales CSIC-UPV/EHU-MPC and DIPC, Av. Tolosa 72, 20018 San Sebastián, Spain
⁵ Department of Physics and Astronomy, University College London, Gower Street, London, WC1E 6BT, UK
⁶ London Centre for Nanotechnology, 17-19 Gordon Street, London, WC1H 0AH, UK
⁷ Department of Materials, Imperial College London, South Kensington Campus, London, SW7 2AZ, UK
⁸ Department of Physics, Imperial College London, South Kensington Campus, London, SW7 2AZ, UK

Corresponding author: ^a a.horsfield@imperial.ac.uk

Received: 7 May 2010
Revised: 17 August 2010
Published online: 1 October 2010

Abstract

Here we survey the theory and applications of a family of methods (correlated electron-ion dynamics, or CEID) that can be applied to a diverse range of problems involving the non-adiabatic exchange of energy between electrons and nuclei. The simplest method, which is a paradigm for the others, is Ehrenfest Dynamics. This is applied to radiation damage in metals and the evolution of excited states in conjugated polymers. It is unable to reproduce the correct heating of nuclei by current carrying electrons, so we introduce a moment expansion that allows us to restore the spontaneous emission of phonons. Because of the widespread use of Non-Equilibrium Green's Functions for computing electric currents in nanoscale systems, we present a comparison of this formalism with that of CEID with open boundaries. When there is strong coupling between electrons and nuclei, the moment expansion does not converge. We thus conclude with a reworking of the CEID formalism that converges systematically and in a stable manner.