Beyond ehrenfest: correlated non-adiabatic molecular dynamics

A. P. HORSFIELD; D. R. BOWLER; A. J. FISHER; T. N. TODOROV; C. G. SANCHEZ

JOURNAL OF PHYSICS CONDENSED MATTER

Institute of Physics

Año: 2004 vol. 16 p. 8251 - 8266

0953-8984

A method for introducing correlations between electrons and ions that iscomputationally affordable is described. The central assumption is that theionic wavefunctions are narrow, which makes possible a moment expansionfor the full density matrix. To make the problem tractable we reduce theremaining many-electron problem to a single-electron problem by performinga trace over all electronic degrees of freedom except one. This introducesboth one- and two-electron quantities into the equations of motion. Quantitiesdepending on more than one electron are removed by making a Hartree–Fockapproximation. Using the first-moment approximation,we perform a number oftight binding simulations of the effect of an electric current on a mobile atom.The classical contribution to the ionic kinetic energy exhibits cooling and isindependent of the bias. The quantum contribution exhibits strong heating,with the heating rate proportional to the bias. However, increased scatteringof electrons with increasing ionic kinetic energy is not observed. This effectrequires the introduction of the second moment.