Chemistry from hot electrons

The conditions (l)-(3) above for the validity of the BOA give some indication as to when its breakdown is most likely to be important in chemical dynamics. For example, very high velocities, e.g., hyperthermal atoms or high vibrational states interacting with surfaces, should promote non-adiabatic contributions to the 

Because there is damping of nuclear motion into e-h pairs, excited e-h pairs at electron temperature Te must also be able to excite nuclear coordinates by fluctuating forces Fx that satisfy the second fluctuation dissipation theorem given as 

Including 7]xx and Fx in Langevin-type classical dynamics has been termed molecular dynamics with electronic frictions (MDEF) [70], and has now been used in several simulations of non-adiabatic dynamics. Of course, the key unknown is the magnitude of the electronic frictions (since they also determine Fx). 

Fortunately, the same limiting conditions that validate the friction approximation can also be used with time-dependent density functional theory to give a theoretical description of rjxx. This expression was originally derived to describe vibrational damping of molecules adsorbed on surfaces [71]. It was later shown to also be applicable to any molecular or external coordinate and at any location on the PES, and thus more generally applicable to non-adiabatic dynamics at surfaces [68,72]. The expression is 

When the limiting conditions of the friction approximation are not valid, e.g., there is strong non-adiabatic coupling or rapid temporal variation of the coupling, there is at present no well-defined first principles method to calculate the breakdown in the BOA. The fundamental problem is that DFT cannot calculate excited states of adsorbates and quantum chemistry techniques, that can in principle calculate excited states, are not possible for extended systems. 

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