Ab initio non-adiabatic molecular dynamics

Abstract

Adiabatic nuclear potential energy surfaces (PESs) defined via the Born-Oppenheimer (BO) approximation are a fundamental concept underlying chemical reactivity theory. For a wide range of excited-state phenomena such as radiationless decay, energy and charge transfer, and photochemical reactions, the BO approximation breaks down due to strong couplings between two or more BO PESs. Non-adiabatic molecular dynamics (NAMD) is the method of choice to model these processes. We review new developments in quantum-classical dynamics, analytical derivative methods, and time-dependent density functional theory (TDDFT) which have lead to a dramatic expansion of the scope of ab initio NAMD simulations for molecular systems in recent years. We focus on atom-centered Gaussian basis sets allowing highly efficient simulations for molecules and clusters, especially in conjunction with hybrid density functionals. Using analytical derivative techniques, forces and derivative couplings can be obtained with machine precision in a given basis set, which is crucial for accurate and stable dynamics. We illustrate the performance of surface-hopping TDDFT for photochemical reactions of the lowest singlet excited states of cyclohexadiene, several vitamin D derivatives, and a bicyclic cyclobutene. With few exceptions, the calculated quantum yields and excited state lifetimes agree qualitatively with experiment. For systems with ∼50 atoms, the present Turbomole implementation allows NAMD simulations with 0.2-0.4 ns total simulation time using hybrid density functionals and polarized double zeta valence basis sets on medium-size compute clusters. We close by discussing open problems and future directions.

Cyclohexadiene Revisited: A Time-Resolved Photoelectron Spectroscopy and ab Initio Study

“…53 Non-adiabatic molecular dynamics (MD) were carried out with the TDDFT-SH implementation. 30,44 All calculations employed the def2-SVP 54 basis set and the PBE0 55, 56 hybrid exchange correlation functional. For CHD, usage of the larger basis sets def2-TZVP 54 and aug-cc-pVTZ 57, 58 leads to excitation energies that are 0.14 and 0.22 eV higher than the def2-SVP results.…”

Modelling materials for solar fuel synthesis by artificial photosynthesis; predicting the optical, electronic and redox properties of photocatalysts

“…presence of defects), finally, can be approximated when using TD-DFT, and when neglecting radiationless de-excitation via internal conversion, from the oscillator strength of the corresponding excitation via Einstein's equation for spontaneous emission. Calculation of the dark contribution to the exciton lifetime and of (exciton) dynamics in general requires non-adiabatic dynamics calculations, which explicitly take into account the coupling between the different energy surfaces [128][129][130][131][132][133][134][135][136]. Such calculations, however, are for the moment rather far from routine.…”

Ab Initio Multiple Spawning Photochemical Dynamics of DMABN Using GPUs

“…The combination of LR-TDDFT and nonadiabatic dynamics has a rather long history and the interested reader is referred to previous reviews for more details. [58][59][60] Our focus on DMABN allows us to sidestep the formal difficulties that LR-TDDFT has with S 0 /S 1 conical intersections, since the interesting nonadiabatic dynamics in this molecule involves transitions between S 2 and S 1 . Of course, nonradiative transitions from S 1 to S 0 are also possible, but on a much longer (many picosecond) time scale that we do not address here.…”