Centre for Computational Chemistry, School of Chemistry , University of Bristol , Bristol BS8 1TS , United Kingdom.
J Chem Theory Comput. 2018 Sep 11;14(9):4590-4599. doi: 10.1021/acs.jctc.8b00337. Epub 2018 Aug 30.
We present Unsöld-W12 (UW12), an approximation to the correlation energy of molecules that is an explicit functional of the single-particle reduced-density matrix. The approximation resembles one part of modern explicitly correlated second-order Møller-Plesset (MP2) theory and is intended as an alternative to MP2 in double-hybrid exchange-correlation functionals. Orbital optimization with UW12 is straightforward, and the UW12 energy is evaluated without a double summation over unoccupied orbitals, leading to a faster basis-set convergence than is seen in double-hybrid functionals. We suggest a one-parameter hybrid exchange-correlation functional XCH-BLYP-UW12. XCH-BLYP-UW12 is similar to double-hybrid functionals, but contains UW12 correlation instead of MP2 correlation. We find that XCH-BLYP-UW12 is more accurate than the existing double-hybrid functional B2-PLYP for small-molecule main-group reaction barrier heights and has roughly the same accuracy as the existing hybrid functional B3LYP for atomization energies.
我们提出了 Unsöld-W12（UW12），这是一种分子相关能量的近似值，是单粒子约化密度矩阵的显函数。该近似类似于现代显式相关二阶 Møller-Plesset（MP2）理论的一部分，旨在替代双杂交交换相关泛函中的 MP2。使用 UW12 进行轨道优化很简单，并且无需对未占据轨道进行双重求和即可评估 UW12 能量，这导致基组收敛速度比双杂交泛函更快。我们建议使用一个参数混合交换相关泛函 XCH-BLYP-UW12。XCH-BLYP-UW12 类似于双杂交泛函，但包含 UW12 相关而不是 MP2 相关。我们发现，对于小分子主族反应势垒高度，XCH-BLYP-UW12 比现有的双杂交泛函 B2-PLYP 更准确，并且对于原子化能，其准确性大致与现有的混合泛函 B3LYP 相当。
