Ring polymer molecular dynamics beyond the linear response regime:Excess electron injection and trapping in liquids

摘要

Ring polymer molecular dynamics (RPMD) is used to directly simulate the injection and relaxationof excess electrons into supercritical helium fluid and ambient liquid water. A method formodulating the initial energy of the excess electron in the RPMD model is presented and used tostudy both low-energy (cold) and high-energy (hot) electron injections. For cold injection into bothsolvents, the RPMD model recovers electronically adiabatic dynamics with the excess electron in itsground state, whereas for hot electron injection, the model predicts slower relaxation dynamicsassociated with electronic transitions between solvent cavities. The analysis of solvent dynamicsduring electron localization reveals the formation of an outgoing solvent compression wave inhelium that travels for over 2 nm and the delayed formation of water solvation shells on thetimescale of 300 fs. Various system-size effects that are intrinsic to the simulation of excess electroninjection are discussed. Comparison of the RPMD simulations with previous mixedquantum-classical dynamics simulations finds general agreement for both the mechanisms andtimescales for electron localization, although the electron localization dynamics in the RPMD modelis essentially completed within 400 fs in helium and 150 fs in water.