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Charge-transfer workshop wrap-up

Dr Rika Kobayashi, NCI Academic Consultant in Computational ChemistryCT workshop

Earlier this month, I presented at the CECAM workshop: “Charge Transfer Modeling in Chemistry: new methods and solutions for a long-standing problem” attended by researchers from all over the world.

Charge-transfer (CT) interactions have long been known to be an important chemical phenomenon e.g. governing photosynthetic processes of plants and bacteria, controlling molecular switches and photovoltaic devices or the functioning of organic dyes. However, these systems are still not satisfactorily modelled or understood from a theoretical chemistry viewpoint. Currently existing high-accuracy methods are too expensive to tackle many problem sizes of interest and even up to a decade ago popular density functional method failed to model these effects correctly.

Dreuw and Head-Gordon [1] highlighted thepresence of spurious low-lying CT states in a zincbacteriochlorin–bacteriochlorin complex: a model system for studying energy transfer in photosynthesis. In 2006 we could show that this could be overcome by what has now become the class of range-separated functionals [2]. The success of this paper prompted a request to organise a workshop on the topic. The aim of the workshop was to bring together researchers covering different perspectives of CT, which are normally developed within different communities and often applied to very different fields.

Core aspects discussed during the workshop were methodology, SAC-CI, the very promising GW-BS method and thelatest developments in density functionals.

Don Truhlar introduced M15-L which he says is the best functional he has designed yet and the closest he has ever come to a universal functional.

Extensive discussion on periodic systems compared the merits of plane-wave approaches versus local basis set methods, finding the latter to be slowly gaining popularity.

Other large systems indicated increasing interest in the viability of embedding methods as discussed by Luuk Visscher [3].

The modification of CT properties by solvents in CT systems highlighted the importance of such treatments and Benedetta Mennucci revealed that the description of solvent effects upon excited state molecules must be treated differently giving significant improvements.

There were many interesting applications to biological systems and solid-state devices, in particular a computational study of photo-induced water splitting which could be important for fuel generation in the future [4].

The wealth of material covered has encouraged us to devote a special issue in Theoretical Chemistry Accounts to CT which we hope will provide an invaluable reference for anyone interested in the field. If you are interested in contributing a paper to this special issue please contact me at by 31 May.

1. A. Dreuw, M. Head-Gordon, J. Am. Chem. Soc. 126 (2004) 4007.
2.  R. Kobayashi and R. D. Amos, Chem. Phys. Letters 420, 106 (2006).
3. M. Pavanello, J. Neugebauer, J. Chem. Phys. 135 (2011) 234103.
4. S.T.A.G. Melissen, F. Labat, P. Sautet, T. Le Bahers, Phys. Chem. Chem. Phys. 2015, 17, 2199.

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