强关联的活性空间对2电子约化密度矩阵理论
Active Space Pair 2-Electron Reduced Density Matrix Theory for Strong Correlation
摘要：
在对近似下，导出并实现了2-电子约化密度矩阵（2-RDM）的活性空间变分计算。对近似只考虑双占用配置的波函数，使计算的2-RDM的计算成本为$\mathcal{O}(r^3)$。计算采用对主动空间组态相互作用（PASCI）方法和对主动空间自洽场（PASSCF）方法。后者包括通过幺正变换的活性和非活性轨道的混合。活性空间对2-RDM方法适用于氮分子，对苯炔双自由基，新合成的双钴配合物，和固氮酶辅因子FeMoco。FeMoco分子在[120，120]活性空间中处理。分数职业在这些系统中的每一个被恢复，表明强电子相关的检测和恢复。
英文摘要：
An active space variational calculation of the 2-electron reduced density matrix (2-RDM) is derived and implemented where the active orbitals are correlated within the pair approximation. The pair approximation considers only doubly occupied configurations of the wavefunction which enables the calculation of the 2-RDM at a computational cost of $\mathcal{O}(r^3)$. Calculations were performed both with the pair active space configuration interaction (PASCI) method and the pair active space self consistent field (PASSCF) method. The latter includes a mixing of the active and inactive orbitals through unitary transformations. The active-space pair 2-RDM method is applied to the nitrogen molecule, the p-benzyne diradical, a newly synthesized BisCobalt complex, and the nitrogenase cofactor FeMoco. The FeMoco molecule is treated in a [120,120] active space. Fractional occupations are recovered in each of these systems, indicating the detection and recovery of strong electron correlation.
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