Virtual Winter School on Computational Chemistry
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Neepa T. Maitra
Professor of PhysicsRutgers University at Newark, Newark, NJ 07102, USA
Time-dependent density functional theory (TDDFT) has achieved an unprecedented balance between accuracy and efficiency in predicting electronic spectra of a wide range of systems in materials science and quantum chemistry. Recent years have seen increasing use for applications beyond linear response, for example, systems driven by laser fields, or prepared in initial states that are not ground-states. At the same time, it has become clear that some phenomena are particularly badly captured by the traditional approximations in TDDFT, and one of these is charge-transfer. This is a bit unfortunate since the transfer of electronic charge is such an important process throughout science. I review what is needed for functional approximations to accurately describe charge transfer. There has been intense progress in the development of functionals that can yield good charge-transfer excitations in many cases, and I will review this. Charge-transfer dynamics, which is a highly non-perturbative process, is an even more challenging problem for TDDFT than just getting the excitation energies correct, requiring density-dependence that is non-local in time, and I review why this is the case. Features of the exact exchange-correlation functional that are essential for this process will be described.
Mark E. Casida
Professeur, chimie théorique, Laboratoire de Chimie Inorganique REdox (CIRE),Département de Chimie Moléculare (DCM, UMR CNRS/UGA 5250), Institut de Chimie Moléculaire de Grenoble(ICMG, FR-2607), Université Grenoble Alpes, 301 rue de la Chimie, CS 40700, 38058 GrenobleCedex 9, FRANCE.
Ordinary density-functional theory (DFT) is restricted to calculating the static electronic energy and density of the electronic ground state. Time-dependent (TD) DFT is a parallel formalism whichallows us to extend the power of DFT to treat time-dependent perturbations. Time-dependent response theory then allows us to calculate absorption spectra from TD-DFT and hence to treat excited states. This formalism is explained at the level of a Masters student, first by setting the stage with a reminder of simple wave function theory for excited states as well as some more advanced ab initio quantum chemistry ideas, and then by focusing on TD-DFT. Some illustrative examples are also presented 1,2 . We also direct the interested reader to highly-cited review articles, including our own 3,4 .
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