Nature of Hops, Coordinates, and Detailed Balance for Nonadiabatic Simulations in the Condensed Phase

Abstract

Photoinduced processes play a crucial role in a multitude of important molecular phenomena. Accurately modeling these processes in an environment other than a vacuum requires a detailed description of the electronic states involved as well as how energy flows are coupled to the surroundings. Nonadiabatic effects must also be included in order to describe the exchange of energy between electronic and nuclear degrees of freedom correctly. In this work, we revisit the ring-opening reaction 1,3-cylohexadiene (CHD) in a solvent environment. Using our newly developed Interface for Non-Adiabatic Quantum mechanics/molecular mechanics in Solvent (INAQS) we trace the evolution of the reaction via hybrid quantum mechanics/molecular mechanics (QM/MM) surface hopping with a focus on the solvent's participation in the nonadiabatic relaxation process and the long-time approach to equilibrium. We explicitly include the MM solvent contribution to the nonadiabatic coupling vector�enabling an accurate approach to equilibrium at long times�and find that in highly multidimensional systems gradients can have little or nothing to do with the nonadiabatic couplings.

Generalized Semiclassical Ehrenfest Method: A Route to Wave Function-Free Photochemistry and Nonadiabatic Dynamics with Only Potential Energies and Gradients

“…The velocity Ṙ a of atom a is adjusted after a K → I hop according to, where h KI,a is the momentum adjustment vector of atom a , and f KI is a factor determined by requiring energy conservation, which requires Inserting eq into gives, where To have a real solution for f KI , the following condition must be fulfilled: When eq is not fulfilled, the called-for a hop is called frustrated, and no hop is made. Although there are arguments that frustrated hops are necessary to achieve detailed balance, − frustrated hops are an intrinsic deficiency of TSH methods; they cause errors such as population leaking. , …”

Ultrafast Photoinduced Dynamics in 1,3-Cyclohexadiene: A Comparison of Trajectory Surface Hopping Schemes†

“…The photochemical interconversion between CHD and 1,3,5-hexatriene (HT), Figure , is one of the most widely studied nonadiabatic processes, both theoretically ,,− and experimentally. ,,,,− This (4n + 2) photoelectrocyclic reaction serves as a simplified model for studying the photophysical and photochemical properties of important macromolecules based on the CHD chromophore. , The interconversion of CHD (isolated) occurs through at least two CIs, and a third CI has been recently proposed as an alternative deactivation path. , This reaction mechanism offers an attractive and complex scenario to compare FSSH and LZSH using a similar level of theory. Our recent theoretical study on this photochemical process using spin-flip time-dependent density functional theory (SF-TDDFT) has successfully described and characterized the most important geometries on the PESs along the ring-opening/closure reaction coordinate, in agreement with those obtained by multireference wave function methods.…”