Frozen natural orbitals for ionized states within equation-of-motion coupled-cluster formalism.
Frozen natural orbitals for ionized states within equation-of-motion coupled-cluster formalism.
复制标题
运动方程耦合团簇形式中电离态的冻结自然轨道。
DOI：
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发表时间：
2010
影响因子：
4.4
通讯作者：
A. Krylov
中科院分区：
文献类型：
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作者：
A. Landau;K. Khistyaev;Stanislav Dolgikh;A. Krylov
将已成功用于基态耦合团簇计算的冻结自然轨道(FNO)方法推广到运动方程耦合团簇(EOM-IP-CC)形式下的开壳层电离电子态。FNOS可以截断虚拟轨道空间，在精度几乎没有下降的情况下显着降低计算成本。介绍了基于MP2的FNO截断方案在EOM-IP-CC中的实现，并使用铍、二氢二聚体、水、水二聚体、氮和尿嘧啶二聚体的电离态进行了基准测试。结果表明，与固定的虚拟轨道保留百分比相比，自然占据阈值，即在截断的虚拟轨道空间中恢复的总自然占据的百分比，提供了更稳健的截断准则。使用99%-99.5%的自然占用阈值，导致虚拟空间减少70%-30%，产生的误差低于1kcal/mol。此外，总能量表现出作为保留的自然占有率的函数的线性相关性，从而允许外推到整个虚拟空间值。通过计算鸟嘌呤的12个最低垂直电离能(IES)和最低绝热电离能，验证了新方法的有效性。除了IE计算外，我们还给出了电离(H(2)O)(2)和(H(2))(2)的势能面扫描。扫描表明，FNO截断没有引入显著的非平行度误差，并准确地描述了PESS形状和相应的能量差，例如解离能。
The frozen natural orbital (FNO) approach, which has been successfully used in ground-state coupled-cluster calculations, is extended to open-shell ionized electronic states within equation-of-motion coupled-cluster (EOM-IP-CC) formalism. FNOs enable truncation of the virtual orbital space significantly reducing the computational cost with a negligible decline in accuracy. Implementation of the MP2-based FNO truncation scheme within EOM-IP-CC is presented and benchmarked using ionized states of beryllium, dihydrogen dimer, water, water dimer, nitrogen, and uracil dimer. The results show that the natural occupation threshold, i.e., percentage of the total natural occupation recovered in the truncated virtual orbital space, provides a more robust truncation criterion as compared to the fixed percentage of virtual orbitals retained. Employing 99%-99.5% natural occupation threshold, which results in the virtual space reduction by 70%-30%, yields errors below 1 kcal/mol. Moreover, the total energies exhibit linear dependence as a function of the percentage of the natural occupation retained allowing for extrapolation to the full virtual space values. The capabilities of the new method are demonstrated by the calculation of the 12 lowest vertical ionization energies (IEs) and the lowest adiabatic IE of guanine. In addition to IE calculations, we present the scans of potential energy surfaces (PESs) for ionized (H(2)O)(2) and (H(2))(2). The scans demonstrate that the FNO truncation does not introduce significant nonparallelity errors and accurately describes the PESs shapes and the corresponding energy differences, e.g., dissociation energies.