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Non-adiabatic Dynamics Using Time-Dependent Density Functional Theory: assessing the Coupling Strengths

Ursula Röthlisberger, Ivano Tavernelli, Enrico Marko Tapavicza
2009
Journal paper
Abstract

Light-driven reactions constitute an important class of processes in physics, chemistry, and biology. The development of accurate and efficient computational tools for the study of excited states dynamics has thus become of primary importance. Recently, we have developed a non-adiabatic ab initio molecular dynamics (AIMD) method, which combines Tully's surface hopping with TDDFT. Here, we investigate some fundamental aspects of this AIMD scheme that deal with the accuracy of TDDFT potential energy surfaces in regions of strong coupling and with the associated intensity of the non-adiabatic couplings (NACs). Of particular interest is the coupling between the ground and the first excited singlet state, which constitute a potential pitfall for all non-adiabatic AND based on TDDFT. To this end, we have investigated the excited state dynamics of protonated formaldimine (CH2NH2+) with particular emphasis on the analysis of the NAC strengths in regions of the configurational space close to surface hopping points and conical intersections. A good agreement of the structural and dynamical properties is found with respect to state averaged multiconfiguration self consistent field results. (C) 2009 Elsevier B.V. All rights reserved.

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Related concepts (28)
Conical intersection
In quantum chemistry, a conical intersection of two or more potential energy surfaces is the set of molecular geometry points where the potential energy surfaces are degenerate (intersect) and the non-adiabatic couplings between these states are non-vanishing. In the vicinity of conical intersections, the Born–Oppenheimer approximation breaks down and the coupling between electronic and nuclear motion becomes important, allowing non-adiabatic processes to take place.
Molecular dynamics
Molecular dynamics (MD) is a computer simulation method for analyzing the physical movements of atoms and molecules. The atoms and molecules are allowed to interact for a fixed period of time, giving a view of the dynamic "evolution" of the system. In the most common version, the trajectories of atoms and molecules are determined by numerically solving Newton's equations of motion for a system of interacting particles, where forces between the particles and their potential energies are often calculated using interatomic potentials or molecular mechanical force fields.
Vibronic coupling
Vibronic coupling (also called nonadiabatic coupling or derivative coupling) in a molecule involves the interaction between electronic and nuclear vibrational motion. The term "vibronic" originates from the combination of the terms "vibrational" and "electronic", denoting the idea that in a molecule, vibrational and electronic interactions are interrelated and influence each other. The magnitude of vibronic coupling reflects the degree of such interrelation.
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