Abstract
Nonadiabatic transitions may be used as a promising tool for dynamical control. However how it could be applied to and affect surface diffusion remains largely unexplored. Here a nonadiabatic model was proposed based on the classical mapping theory to introduce multistate couplings in addition to the bare surface diffusion. By performing nonadiabatic molecular dynamics simulation on a benchmark system of atomic hydrogen diffusion on the Cu (001) surface, it is demonstrated that nonadiabatic transitions could modulate diffusion dynamics in a robust way, i.e. either suppressing or promoting it. Depending on the design for the coupling regime in the nonadiabatic model, simulation results show that aside for the nonadiabatic damping effect, the diffusion constant of H atom could be enhanced by a factor of 2-6 in the temperature range of T = 500-600 K. The effect of nonadiabatic transitions may provide an explanation to the significant discrepancy between experimental measured diffusion constant and previous theoretical predictions. By highlighting the role of nonadiabatic effects, in particular under nonequilibrium conditions, this work sheds light on the development of new molecular control schemes for practical applications.
Highlights
Dynamic control of molecular processes1,2 is one of the ultimate dreams of fundamental research, which may leads to significant advances in a variety of practical applications including nanotechnology, chemical engineering, and materials design
Our case is specific to a particular model for the modified hopping dynamics, we believe that the physical picture obtained here is quite general and nonadiabatic transitions or multistate couplings may be used to control real time dynamics in a robust way, as retardant and as a promoter! our work suggests that a more comprehensive model is called in the investigation of nonadiabatic effects on dynamic control
We propose a molecular nonadiabatic control model based on the classical mapping theory and its recent development to modulate hydrogen diffusion on metal surfaces
Summary
Dynamic control of molecular processes is one of the ultimate dreams of fundamental research, which may leads to significant advances in a variety of practical applications including nanotechnology, chemical engineering, and materials design. We demonstrate within a consistent nonadiabatic framework that the design of nonadiabatic control scheme may lead to a robust modulation (i.e. either enhance or suppress) on surface diffusion. First a coupled multistate (nonadiabatic) model for surface diffusion was proposed in terms of localized diabatic states, based on the classical mapping theory, which allows for state-specific properties and consistent electronic-nuclear motions to be incorporated. We perform the real time nonadiabatic molecular dynamics simulation of atomic hydrogen diffusion on the Cu (001) surface, and investigate the nonadiabatic effects on surface diffusion upon the nonequilibrium switch-on of additional multistate modification on equilibrium dynamics, for two types of nonadiabatic couplings models. In addition to the conventional damping effect, more interestingly about 2-6 folds speedup in H diffusion dynamics in the relatively high temperature range of 500-600K was observed, which suggests a novel nonadiabatic control mechanism for surface dynamics. This work provides a possible explanation to reconcile the significant discrepancy between the experimentally measured facile surface diffusion and the theoretical predictions based on calculations and simulations without fully consideration of nonadiabatic transitions
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