Selected Topics of the Theory of Chemical Elementary Processes

First Principles Molecular Dynamics Involving Excited States and Nonadiabatic Transitions

“…The simplest and computationally least expensive way of incorporating nonadiabatic effects is by describing nuclear motion by classical mechanics and only the electrons quantum mechanically. In these so-called mixed quantum-classical approaches (often also referred to as semiclassical approaches), [139][140][141][142][143][144][145][146][147][148] the atomic nuclei follow some trajectory R(t) while the electronic motion is captured by some timedependent total wavefunction Ψ(r; t) satisfying the time-dependent electronic Schrödinger equation…”

Optical, Mechanical, and Opto‐Mechanical Switching of Anchored Dithioazobenzene Bridges

“…According to nonadiabatic theory, [30] an important criterion controlling the efficiency of nonradiative S 1 !S 0 decay back to the ground state, thus affecting the quantum yield of the opto-mechanical switching process, is the S 1 -S 0 energy gap (E gap ) at a given instantaneous configuration. In order to extract trends relating to the efficiency of nonradiative decay pathways at the different elongations, we computed the time averages E gap over the 0.5 ps excited-state trajectories for simulations starting from both isomers (Figure 4).…”

Theoretical approach to reactions of polyatomic molecules

“…In what follows we concentrate our discussion mainly on the problems connected with steps I and 11, and to simplify matters, we adopt an electronically adiabatic approximation, i.e., one fixed electronic state i of the whole interacting system. In the (pointwise) generation of the potential energy functions U,(X) = VM(X) + E f ( X ) (2) for chosen sets X = {X,,X2, . .…”

“…This reduces the rate constants by about one order of magnitude or more. Finally we replace the theoretical value of the bond dissociation energy by the experimental one, thus eliminating the major part of the deficiency (2). A selected number of adiabatic rovibrational terms constructed in such a scheme is shown in Figure 4.…”

“…For developing conceptually transparent and computationally feasible theoretical models one may restrict the treatment (1) to that part of the nuclear configuration space which is energetically relevant ("static" reduction) and (2) to that subset of the total set of the degrees of freedom, i.e., a subspace of the nuclear configuration space which is dynamically relevant ("dynamical" or "dimensional" reduction). The former reduction can be accomplished by the concept of the reaction path, the latter by consideration of the couplings between the modes of motion.…”