Nakatani Kaho, Nakatani Naoki
Department of Chemistry, Tokyo Metropolitan University, 1-1, Minami-Osawa, Hachioji 192-0397, Japan.
J Chem Phys. 2025 Jul 21;163(3). doi: 10.1063/5.0273486.
Ab initio variational treatment of the antisymmetrized product of strongly orthogonal geminals (APSG) allowing for full mixing of singlet and triplet geminals, presented in our previous study [Nakatani and Sato, J. Chem. Phys. 158, 211104 (2023)], was reformulated and extended according to the group function model. A key feature of the reformulation lies in the construction of strongly orthogonal geminals or group functions using general spinorbitals, which allows us to describe strong correlation through breaking both Ŝ2 and Ŝz symmetries while maintaining the simplicity of the trial wave functions and variational equations. Numerical analysis of correlated hydrogen clusters suggested that a noncollinear spin state cannot be the ground state in the APSG model. In some cases, when group functions for an odd number of electrons are used, on the other hand, symmetry breaking was observed for a spin-unrestricted, collinear state, and an obtained ground state was noncollinear. The present framework clearly detects instabilities of geminals and group functions and also provides effective reference states for the strongly correlated regime.
我们先前的研究[Nakatani和Sato，《化学物理杂志》158, 211104 (2023)]中提出的对强正交双电子对反对称积（APSG）的从头算变分处理允许单重态和三重态双电子对完全混合，根据群函数模型进行了重新表述和扩展。重新表述的一个关键特征在于使用一般自旋轨道构建强正交双电子对或群函数，这使我们能够通过打破(Ŝ^2)和(Ŝ_z)对称性来描述强关联，同时保持试探波函数和变分方程的简单性。对相关氢簇的数值分析表明，在APSG模型中，非共线自旋态不可能是基态。另一方面，在某些情况下，当使用奇数个电子的群函数时，观察到自旋非限制共线态的对称性破缺，并且得到的基态是非共线的。当前框架清楚地检测到双电子对和群函数的不稳定性，并且还为强关联区域提供了有效的参考态。
