Coupling between Thermochemical Contributions of Subvalence Correlation and of Higher-Order Post-CCSD(T) Correlation EffectsA Step toward “W5 Theory”

We consider the thermochemical impact of post-CCSD(T)
contributions
to the total atomization energy (TAE, the sum of all bond energies)
of first- and second-row molecules, and specifically their coupling
with the subvalence correlation contribution. In particular, we find
large contributions from (Q) when there are several neighboring second-row
atoms. Otherwise, both higher-order triples T3–(T) and connected quadruples (Q) are important in
systems with strong static correlation. Reoptimization of the reference
geometry for core–valence correlation increases the calculated
TAE across the board, most pronouncedly for second-row compounds with
neighboring second-row atoms. We present a first proposal for a “W5
theory” protocol and compare computed TAEs for the W4-08 benchmark
with prior reference values. For some key second-row species, the
new values represent nontrivial revisions. Our predicted TAE0 values (TAE at 0 K) agree well with the ATcT (Active Thermochemical
Tables) values, including for the very recent expansion of the ATcT
network to boron, silicon, and sulfur compounds.

本研究考察了后CCSD(T)（post-CCSD(T)）贡献对第一、第二周期分子总原子化能（total atomization energy，缩写TAE，即所有键能之和）的热化学影响，重点探讨其与亚价层相关贡献（subvalence correlation contribution）的耦合效应。具体而言，当体系中存在多个相邻的第二周期原子时，(Q)项的贡献较为显著。反之，在存在强静态相关的体系中，高阶三重激发项T3–(T)与连接型四重激发(Q)均具有重要作用。对核价相关（core–valence correlation）的参考几何构型（reference geometry）进行再优化后，所有体系的计算总原子化能均有所提升，其中对含有相邻第二周期原子的第二周期化合物的影响最为突出。本研究首次提出了“W5理论”（W5 theory）方案，并将W4-08基准测试集（W4-08 benchmark）的计算总原子化能与此前的参考值进行了对比。针对部分关键第二周期物种，新的计算值实现了实质性修正。我们预测的TAE₀值（0 K下的总原子化能）与活化热化学表（Active Thermochemical Tables，简称ATcT）的数值吻合良好，这也包括近期ATcT数据库扩展至硼、硅及硫化合物的相关结果。