Molecular dynamics with electronic friction

Fig. 3. Vibrational population distributions of N2 formed in associative desorption of N-atoms from ruthenium, (a) Predictions of a classical trajectory based theory adhering to the Born-Oppenheimer approximation, (b) Predictions of a molecular dynamics with electron friction theory taking into account interactions of the reacting molecule with the electron bath, (c) Born—Oppenheimer potential energy surface, (d) Experimentally-observed distribution. The qualitative failure of the electronically adiabatic approach provides some of the best available evidence that chemical reactions at metal surfaces are subject to strong electronically nonadiabatic influences. (See Refs. 44 and 45.)...

MDEF Molecular Dynamics with Electronic Frictions... 

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). 

Figure 3.28. N2 vibrational state distribution in associative desorption from Ru(0001). (a) Observed in experiment. From Ref. [126]. (b) From 3D (Z, R, q) first principles quasi-classical dynamics, with the solid triangles pointing upward being adiabatic dynamics and the squares from molecular dynamics with electronic frictions also from DFT. Based on the PES and frictions of Ref. [68]. The open triangles pointing downward are the results of 6D first principles adiabatic quasi-classical dynamics from Ref. [253].

Figure 3.41. Photoyield Y for H2 and D2 associative desorption from Ru(0001)(l x 1)H and Ru(0001)(lxl)D as a function of absorbed 800 nm 130fs laser pulse fluence F. (a) experimental results with circles for H2 desorption and squares for D2 desorption. Solid lines are fits to a ID friction model and dashed lines are fits to power law expressions, Y oc F28 for H2 and Y oc F3 2 for D2. From Ref. [413]. (b) Equivalent photoyields for associative desorption from 3D first principles molecular dynamics with electronic frictions. From Ref. [101].

Figure 3.43. The time dependent electronic temperature Te, lattice temperature Tq. and adsorbate temperature defined as Tads = [EH /2kB following a 130 fs laser pulse with absorbed laser fluence of 120 J/m2 centered at time t = 0. The bar graph is the rate of associative desorption dY/dt as a function of t. Te and T are from the conventional two temperature model and 7 ads and dY/dl are from 3D first principles molecular dynamics with electronic frictions. From Ref. [101].

Electron-hole pairs have already been treated on the Hartree-Fock level in otherwise classical high-dimensional molecular dynamics simulation using the molecular dynamics with electronic friction method [120]. In this approach, the energy transfer between nuclear degrees of freedom and the electron bath of the surface is also modelled with a position-dependent friction term, but additionally temperature-dependent fluctuating forces are included. 

Head-Gordon, M., TuUy, J.G. Molecular dynamics with electronic frictions, J. Chem. Phys. 1995, 103,10137. 

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