Strongly contracted canonical transformation theory.
Strongly contracted canonical transformation theory.
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DOI：
10.1063/1.3274822
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发表时间：
2010-01
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影响因子：
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通讯作者：
Eric Neuscamman;Takeshi Yanai;G. Chan
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文献类型：
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作者：
Eric Neuscamman;Takeshi Yanai;G. Chan
正则变换（CT）理论描述了具有大活动空间的多参考系统中的动态相关。在这里，我们讨论CT理论的入侵状态问题，为什么我们以前的重叠矩阵截断的方法变得不可行，足够大的活动空间。我们建议使用强和弱收缩的激发算子作为替代处理入侵者状态的CT理论。对H（2）O、N（2）和NiO分子计算了这些算符的性能，并与完整的活性空间二阶微扰理论和Davidson修正的多参考组态相互作用理论进行了比较.最后，使用强压缩CT理论和轨道优化的密度矩阵重整化群理论的组合，我们评估的单重态-三重态间隙的自由碱卟啉使用的活性空间包含所有24个平面外的2 p轨道。目前，只有使用CT理论才能对这种大小的活动空间的动态相关性进行建模。
Canonical transformation (CT) theory describes dynamic correlation in multireference systems with large active spaces. Here we discuss CT theory's intruder state problem and why our previous approach of overlap matrix truncation becomes infeasible for sufficiently large active spaces. We propose the use of strongly and weakly contracted excitation operators as alternatives for dealing with intruder states in CT theory. The performance of these operators is evaluated for the H(2)O, N(2), and NiO molecules, with comparisons made to complete active space second order perturbation theory and Davidson-corrected multireference configuration interaction theory. Finally, using a combination of strongly contracted CT theory and orbital-optimized density matrix renormalization group theory, we evaluate the singlet-triplet gap of free base porphin using an active space containing all 24 out-of-plane 2p orbitals. Modeling dynamic correlation with an active space of this size is currently only possible using CT theory.