Near-Exact CCSDT Energetics from Rank-Reduced Formalism Supplemented by Non-iterative Corrections
Near-Exact CCSDT Energetics from Rank-Reduced Formalism Supplemented by Non-iterative Corrections
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DOI：
10.1021/acs.jctc.1c00933
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发表时间：
2021-12-14
影响因子：
5.5
通讯作者：
Lesiuk, Michal
中科院分区：
文献类型：
--
作者：
Lesiuk, Michal
我们引入了一个非迭代的能量修正，它是在降阶耦合簇方法的基础上加入的，它考虑了母体三重激发子空间中排除的激发。利用耦合簇拉格朗日形式推导了修正公式，并假定在Fock算子的作用下母体激发子空间是封闭的。由于三次激励幅值张量的降阶形式，计算校正标度的计算成本为N-7，其中N是系统大小。从总相关能量和相对相关能量两个方面评估了该方法的精度和计算效率。我们证明了非迭代校正可以起到两种不同的作用。如果kJ/摩尔分数的精度水平对于给定的系统是足够的，则校正显著降低了计算的迭代部分所需的母体三激发子空间的维度。同时，它使准确的CCSDT结果能够重现到0.1kJ/mol以下的精度水平，具有更大的但仍然合理的母体激发子空间的维度。这通常可以以比CCSD(T)方法所需的计算成本大几倍的计算代价来实现。该方法保留了单参考耦合团簇理论的黑箱特征；母激发子空间的维度仍然是唯一需要指定的附加参数。
We introduce a non-iterative energy correction, added on top of the rank-reduced coupled-cluster method with single, double, and triple substitutions, that accounts for excitations excluded from the parent triple excitation subspace. The formula for the correction is derived by employing the coupled-cluster Lagrangian formalism, with an additional assumption that the parent excitation subspace is closed under the action of the Fock operator. Owing to the rank-reduced form of the triple excitation amplitudes tensor, the computational cost of evaluating the correction scales as N-7, where N is the system size. The accuracy and computational efficiency of the proposed method is assessed for both total and relative correlation energies. We show that the non-iterative correction can fulfill two separate roles. If the accuracy level of a fraction of kJ/mol is sufficient for a given system, the correction significantly reduces the dimension of the parent triple excitation subspace needed in the iterative part of the calculations. Simultaneously, it enables reproducing the exact CCSDT results to an accuracy level below 0.1 kJ/mol, with a larger, yet still reasonable, dimension of the parent excitation subspace. This typically can be achieved at a computational cost only several times larger than required for the CCSD(T) method. The proposed method retains the black-box features of the single-reference coupled-cluster theory; the dimension of the parent excitation subspace remains the only additional parameter that has to be specified.