用范德华密度泛函改进质子转移势垒：排斥非局域关联的作用
Improved proton-transfer barriers with van der Waals density functionals: Role of repulsive non-local correlation
摘要：
有机络合物间的质子转移是一种常见而重要的生物化学过程。不幸的是，PT能垒很难准确预测使用密度泛函理论（DFT），特别是，广义梯度近似（GGA）往往低估PT障碍。此外，PT通常发生在色散力有助于系统凝聚力的环境中;因此，合适的交换相关泛函应该准确地描述色散力和PT屏障。本文提供了基准结果的PT障碍的几个密度泛函，包括几个变种的范德华密度泛函（vdWDF）。基准组包括具有分子间和分子内PT的小有机分子。结果表明，用完全非局域的vdw-DF关联代替GGA关联增加了PT势垒，使其更接近量子化学参考值。相比之下，包括非局部相关与Vydrov-Voorhis（VV）方法或DFT-D3或Tkatchenko-Scheffler（TS）水平的色散校正几乎没有任何影响的PT障碍。混合泛函也增加和改善能量，并且最佳性能由一致交换范德华密度泛函vdw-DF-cx的混合版本提供。对于甲酸二聚体PT体系，我们分析了GGA交换和非局域关联的贡献。分析表明，非局域相关核的排斥部分在用vdw-DF预测的PT能垒中起着关键作用。
英文摘要：
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, 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 (vdWDF). 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 nonlocal correlations with the Vydrov-Voorhis (VV) method or dispersion-corrections at the DFT-D3 or the Tkatchenko-Scheffler (TS) level has barely any impact on the PT barriers. Hybrid functionals also increase and improve the energies and the best performance is provided by a hybrid version of the consistent-exchange van der Waals density functional vdW-DF-cx. 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.
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