https://doi.org/10.1140/epjb/e2013-40047-x
Regular Article
Towards time-dependent, non-equilibrium charge-transfer force fields
Contact electrification and history-dependent dissociation limits
1
Jülich Supercomputing Centre, Institute for Advanced
Simulation, FZ
Jülich, 52425
Jülich,
Germany
2
Department of Materials Science and Engineering, Universität des
Saarlandes, 66123
Saarbrücken,
Germany
a e-mail: martin.mueser@mx.uni-saarland.de
Received:
22
January
2013
Received in final form:
10
May
2013
Published online:
30
July
2013
Force fields uniquely assign interatomic forces for a given set of atomic coordinates. The underlying assumption is that electrons are in their quantum-mechanical ground state or in thermal equilibrium. However, there is an abundance of cases where this is unjustified because the system is only locally in equilibrium. In particular, the fractional charges of atoms, clusters, or solids tend to not only depend on atomic positions but also on how the system reached its state. For example, the charge of an isolated solid – and thus the forces between atoms in that solid – usually depends on the counterbody with which it has last formed contact. Similarly, the charge of an atom, resulting from the dissociation of a molecule, can differ for different solvents in which the dissociation took place. In this paper we demonstrate that such charge-transfer history effects can be accounted for by assigning discrete oxidation states to atoms. With our method, an atom can donate an integer charge to another, nearby atom to change its oxidation state as in a redox reaction. In addition to integer charges, atoms can exchange “partial charges” which are determined with the split charge equilibration method.
Key words: Computational Methods
© EDP Sciences, Società Italiana di Fisica and Springer-Verlag, 2013