On the Combination of TDDFT with Molecular Dynamics: New Developments

Abstract

In principle, we should not need the time-dependent extension of density-functional theory (TDDFT) for excitations, and in particular not for Molecular Dynamics (MD) studies: the theorem by Hohenberg and Kohn teaches us that for any observable that we wish to look at (including dynamical properties or observables dependent on excited states) there is a corresponding functional of the ground-state density. Yet the unavailability of such magic functionals in many cases (the theorem is a non-constructive existence result) demands the development and use of the alternative exact reformulation of quantum mechanics provided by TDDFT. This theory defines a convenient route to electronic excitations and to the dynamics of a many-electron system subject to an arbitrary time-dependent perturbation. This is, in fact, the main purpose of inscribing TDDFT in a MD framework -the inclusion of the effect of electronic excited states in the dynamics. However, as we will show in this review, it may not be the only use of TDDFT in this context. In this manuscript, we review two recent proposals: In Section 1.2, we show how TDDFT can be used to design efficient gsBOMD algorithms -even if the electronic excited states are in this case not relevant. The work described in Section 1.3 addresses the problem of mixed quantum-classical systems at thermal equilibrium.Comment: 10 pages, 1 figure, to be published in the book "Time Dependent Density Functional Theory" by Springer Verla

Polaritonic Chemistry: Collective Strong Coupling Implies Strong Local Modification of Chemical Properties

“…Overall, our findings open the door to include a multitude of quantum chemical concepts and methods into the polaritonic chemistry context, which were successfully developed and applied over the past decades. For example, one can give up our initial dilute system assumptions and start to investigate more realistic and complex chemical setups by including, for example temperature, electron overlap, different orientations, solvent effects, driving laser fields, and much more. , This paves the way to many novel discoveries and applications based on ab initio polaritonic chemistry methods, all of which nurture the hope that by collective strong coupling, unprecedented local control of chemical processes may become within reach.…”

Photo-Induced Coupled Nuclear and Electron Dynamics in the Nucleobase Uracil

“…Most methods which can describe the electron dynamics are often modified versions of their well-known quantumchemical counter parts and neglect the influence of the nuclear motion [19][20][21][22][23] or treat it classically [24][25][26][27]. One of the possibilities to treat both the nuclear and the electron dynamics in a molecular systems is the quantum-mechanical NEMol ansatz [28][29][30][31][32].…”

Coupled nuclear and electron dynamics in the vicinity of a conical intersection

“…Further techniques are based on the coupled propagation of the nuclear and electronic wavefunction on a single time-dependent potential energy surface [30][31][32][33] . But for larger molecular systems the main techniques used are mixed quantum classical representations [34][35][36][37] . For example, the electron dynamics is described using TD-DFT and the nuclear motion is considered using an Ehrenfest approach 34,35 .…”

“…But for larger molecular systems the main techniques used are mixed quantum classical representations [34][35][36][37] . For example, the electron dynamics is described using TD-DFT and the nuclear motion is considered using an Ehrenfest approach 34,35 . But these methods do not reflect the quantum nature of the nuclei which, however, becomes important for ultrashort pulse excitation and nonadiabatic transitions.…”