A pair natural orbital implementation of the coupled cluster model CC2 for excitation energies
A pair natural orbital implementation of the coupled cluster model CC2 for excitation energies
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DOI：
10.1063/1.4819071
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发表时间：
2013-08-28
影响因子：
4.4
通讯作者：
Haettig, Christof
中科院分区：
文献类型：
--
作者：
Helmich, Benjamin;Haettig, Christof
我们演示了如何扩展对自然轨道（PNO）方法的激发态，在以前的工作中提出的微扰双校正配置相互作用单打（CIS（D）），迭代耦合集群方法，如近似单打和双打模型CC 2。PNO构造的原始O（N-5）标度通过使用轨道特定虚（OSV）作为中间步骤而减少，而不破坏PNO方法的初始精度。此外，一个较慢的误差收敛的电荷转移状态进行了分析和解决的数值拉普拉斯变换过程中的PNO建设，使一个同样准确的治疗本地和电荷转移激发实现。与特定状态的截断PNO的扩展，本征值问题的解决相结合的戴维森算法与紧缩，以投影出已经确定的根和自动刷新与一代新的PNO，以实现自一致性的PNO空间。对于大的测试集，我们发现PNO-CC 2激发能的截断误差仅略大于PNO-CIS（D）。PNO-CC 2的计算效率被证明为一个大的有机染料，其中减少了一倍的空间由一个因素超过1000相比，得到的正则计算。仅通过统一的OSV空间就可以实现将加倍空间压缩30倍。此外，在一系列甘氨酸低聚物上使用仍然初步的PNO-CC 2实施的计算揭示了在100和300个基函数之间使用规范RI-CC 2实施的早期盈亏平衡点。(C)2013 AIP Publishing LLC.
We demonstrate how to extend the pair natural orbital (PNO) methodology for excited states, presented in a previous work for the perturbative doubles correction to configuration interaction singles (CIS(D)), to iterative coupled cluster methods such as the approximate singles and doubles model CC2. The original O(N-5) scaling of the PNO construction is reduced by using orbital-specific virtuals (OSVs) as an intermediate step without spoiling the initial accuracy of the PNO method. Furthermore, a slower error convergence for charge-transfer states is analyzed and resolved by a numerical Laplace transformation during the PNO construction, so that an equally accurate treatment of local and charge-transfer excitations is achieved. With state-specific truncated PNO expansions, the eigenvalue problem is solved by combining the Davidson algorithm with deflation to project out roots that have already been determined and an automated refresh with a generation of new PNOs to achieve self-consistency of the PNO space. For a large test set, we found that truncation errors for PNO-CC2 excitation energies are only slightly larger than for PNO-CIS(D). The computational efficiency of PNO-CC2 is demonstrated for a large organic dye, where a reduction of the doubles space by a factor of more than 1000 is obtained compared to the canonical calculation. A compression of the doubles space by a factor 30 is achieved by a unified OSV space only. Moreover, calculations with the still preliminary PNO-CC2 implementation on a series of glycine oligomers revealed an early break even point with a canonical RI-CC2 implementation between 100 and 300 basis functions. (C) 2013 AIP Publishing LLC.