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[1] Popelier, P. L. A.; Brémond, É. A. G. Int.J.Quant.Chem. 2009, 109, 2542.

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Aurélien de la Lande

Laboratoire de Chimie Physique, Université Paris Sud, CNRS, Université Paris Saclay. 15, avenue Jean Perrin, 91405 Orsay, Cedex. France""

Robust, basis-set independent method for the evaluation of charge-transfer energy in nonconvalent complexes

Separation of the energetic contribution of charge transfer to interaction energy in noncovalent complexes would provide important insight into the mechanisms of the interaction. However, the calculation of charge-transfer energy is not an easy task. It is not a physically well-defined term and the results might depend on how it is described in practice. Commonly, the charge transfer is defined in terms of molecular orbitals; in this framework, however, the charge transfer vanishes as the basis set size increases towards the complete basis set limit. This can be avoided by defining the charge transfer in terms of the spatial extent of the electron densities of the interacting molecules, but the schemes used so far do not reflect the actual electronic structure of each particular system and thus are not reliable. We propose a novel approach – spatial partitioning of the system which is based on a charge transfer-free reference state, namely superimposition of electron densities of the non-interacting fragments. We show that this method, employing constrained DFT for the calculation of the charge-transfer energy, yields reliable results and is robust with respect to the strength of the charge transfer, the basis set size and the DFT functional used. Because it is based on DFT, the method is applicable to rather large systems.

[1] Řezáč, J; de la Lande, A. J. Chem. Theor. Comput. 2015, 11, 528-537.

A. Martín Pendás

Universidad de Oviedo, Julian Claveria, 33006, Oviedo, Spain

Electron distribution functions from academic models: towards a real space Aufbau principle

Electron number distribution functions (EDFs) allow for the computation of the weights of real space resonance structures. To obtain them we need a partition of space into chemically meaningul regions, i.e. through QTAIM, ELF, Hirshfeld, or any other exhaustive or fuzzy decomposition available in the literature.

With such a decomposition we may compute the probability of distributing the N electrons of a molecular system into the m regions in which we have divided space, in every possible way. EDFs provide valuable insight into chemical bonding, and here we show that they may be successfully approximated by very simple models, giving rise to an interesting interpretation of the standard Aufbau principle in real space. This is obtained from academic models of the wave functions of simple systems and a Mulliken-like condensation.