Řezáč Jan, de la Lande Aurélien
Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic , Flemingovo nám. 2, 166 10 Prague 6, Czech Republic.
Laboratoire de Chimie Physique CNRS UMR 8000, Université Paris-Sud. Bât. 349 , 15, rue Jean Perrin, 91405 Orsay Cedex, France.
J Chem Theory Comput. 2015 Feb 10;11(2):528-37. doi: 10.1021/ct501115m. Epub 2015 Jan 26.
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 toward 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 spatial partitioning of the system, which is based on a charge transfer-free reference state, namely superimposition of electron densities of the noninteracting 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.
分离非共价复合物中电荷转移对相互作用能的能量贡献，将为相互作用机制提供重要见解。然而，计算电荷转移能并非易事。它不是一个物理上定义明确的术语，其结果可能取决于在实际中如何描述它。通常，电荷转移是根据分子轨道来定义的；然而，在此框架下，随着基组大小朝着完全基组极限增加，电荷转移会消失。通过根据相互作用分子电子密度的空间范围来定义电荷转移可以避免这种情况，但迄今为止所使用的方案并不能反映每个特定系统的实际电子结构，因此不可靠。我们提出一种基于无电荷转移参考态（即非相互作用片段电子密度的叠加）的系统空间划分方法。我们表明，这种采用约束密度泛函理论来计算电荷转移能的方法能产生可靠结果，并且在电荷转移强度、基组大小以及所使用的密度泛函理论泛函方面具有稳健性。由于它基于密度泛函理论，该方法适用于相当大的系统。
