Seyedraoufi S, Berland Kristian
Department of Mechanical Engineering and Technology Management, Norwegian University of Life Sciences, Ås, Norway.
J Chem Phys. 2022 Jun 28;156(24):244106. doi: 10.1063/5.0095128.
Proton-transfer (PT) between organic complexes is a common and important biochemical process. Unfortunately, PT energy barriers are difficult to accurately predict using density functional theory (DFT); in particular, using the generalized gradient approximation (GGA) tends to underestimate PT barriers. Moreover, PT typically occurs in environments where dispersion forces contribute to the cohesion of the system; thus, a suitable exchange-correlation functional should accurately describe both dispersion forces and PT barriers. This paper provides benchmark results for the PT barriers of several density functionals, including several variants of the van der Waals density functional (vdW-DF). The benchmark set comprises small organic molecules with inter- and intra-molecular PT. The results show that replacing GGA correlation with a fully non-local vdW-DF correlation increases the PT barriers, making it closer to the quantum chemical reference values. In contrast, including non-local correlations with the Vydrov-Voorhis method or dispersion-corrections at the DFT-D3 or the Tkatchenko-Scheffler level has barely any impact on the PT barriers. Hybrid functionals also increase and improve the energies, resulting in an excellent performance of hybrid versions of vdW-DF-cx and vdW-DF2-B86R. For the formic acid dimer PT system, we analyzed the GGA exchange and non-local correlation contributions. The analysis shows that the repulsive part of the non-local correlation kernel plays a key role in the PT energy barriers predicted with vdW-DF.
有机配合物之间的质子转移（PT）是一种常见且重要的生化过程。不幸的是，使用密度泛函理论（DFT）难以准确预测PT能垒；特别是，使用广义梯度近似（GGA）往往会低估PT能垒。此外，PT通常发生在色散力有助于系统凝聚的环境中；因此，合适的交换相关泛函应能准确描述色散力和PT能垒。本文提供了几种密度泛函（包括范德华密度泛函（vdW-DF）的几种变体）的PT能垒的基准结果。基准集包括具有分子间和分子内PT的小分子。结果表明，用完全非局部的vdW-DF相关取代GGA相关会增加PT能垒，使其更接近量子化学参考值。相比之下，在DFT-D3或Tkatchenko-Scheffler水平上使用Vydrov-Voorhis方法或色散校正包含非局部相关对PT能垒几乎没有任何影响。杂化泛函也会提高能量并改善性能，从而使vdW-DF-cx和vdW-DF2-B86R的杂化版本具有出色的性能。对于甲酸二聚体PT系统，我们分析了GGA交换和非局部相关的贡献。分析表明，非局部相关核的排斥部分在vdW-DF预测的PT能垒中起关键作用。
