Emergence of negative viscosities and colored noise under current-driven Ehrenfest molecular dynamics

Molecules in molecular junctions are subject to current-induced forces that can break chemical bonds, induce reactions, destabilize geometry, and halt the operation of junction. Theories behind current-driven dynamics simulations rely on a perturbative time-scale separation within system with subsequent use nonequilibrium Green's functions (NEGF) compute conservative, non-conservative, stochastic exerted by electrons nuclear degrees freedom. We analyze effectiveness this approximation, paying particular attention phenomenon negative viscosities. The approximation is directly compared Ehrenfest approach. introduce novel time-stepping approach calculate present method via exact integration equations motion for functions, which does not necessitate provides an description corresponding classical dynamics. observe viscosities artifacts treatment but also emerge However, effects viscosity have possibility being overwhelmed predominantly positive dissipation due higher-order unaccounted Additionally, we assess validity white-noise forces, finding it justifiable presence clear more applicable when current-carrying orbital moved outside voltage window. Finally, demonstrate junction models consisting one two