Mihálka Zs É, Noga J
Department of Inorganic Chemistry, Faculty of Natural Sciences, Comenius University in Bratislava, Mlynská dolina, Ilkovičova 6, 842 15 Bratislava 4, Slovakia.
J Chem Theory Comput. 2025 Aug 26;21(16):7765-7781. doi: 10.1021/acs.jctc.5c00264. Epub 2025 Aug 5.
Recent accounts of the good performance of the pair coupled cluster doubles (pCCD) method extended by an explicitly correlated (F12) model in describing essential correlation effects motivated us to further explore pair-function based methodologies in conjunction with the explicitly correlated framework. While pCCD can be reformulated as the antisymmetrized product of interacting two-electron fragments (geminals), driven by the special structure of the resulting reference function, we opt for employing strongly orthogonal geminals in the Ansatz. In this work, the antisymmetrized product of strongly orthogonal geminals wave function (SLG), which is capable of capturing static correlation in a computationally efficient manner, is corrected by an F12 addition via perturbation theory. The explicitly correlated terms of the wave function are internally contracted and are responsible for describing the dynamic correlation missing from SLG, by virtue of incorporating all possible double excitations from the reference. A Slater-type function is used as a correlation factor, while amplitudes obtained from the variational optimization of the Hylleraas-functional as well as those fixed according to the - and -wave cusp conditions (SP-Ansatz) are explored. The presented SLG-F12 model is applied in order to investigate the splitting of the lowest singlet and triplet states in small biradicals and in other multireference systems.
最近有报道称，通过显式相关（F12）模型扩展的双耦合簇（pCCD）方法在描述基本相关效应方面表现良好，这促使我们进一步探索基于对函数的方法与显式相关框架相结合的情况。虽然pCCD可以重新表述为相互作用的双电子片段（双粒子基函数）的反对称积，但受所得参考函数特殊结构的驱动，我们选择在近似中使用强正交双粒子基函数。在这项工作中，能够以计算高效的方式捕捉静态相关的强正交双粒子基函数波函数（SLG）的反对称积，通过微扰理论的F12加法进行校正。波函数的显式相关项进行了内部收缩，并通过纳入来自参考的所有可能的双激发来负责描述SLG中缺失的动态相关。使用斯莱特型函数作为相关因子，同时探索了从海勒拉斯泛函的变分优化获得的振幅以及根据-和-波尖点条件固定的振幅（SP近似）。应用所提出的SLG-F12模型来研究小双自由基和其他多参考系统中最低单重态和三重态的分裂。
