Department of Chemistry, University of Cambridge, Cambridge, United Kingdom.
J Chem Phys. 2017 Sep 28;147(12):124105. doi: 10.1063/1.4991795.
We consider the sampling of the coupled cluster expansion within stochastic coupled cluster theory. Observing the limitations of previous approaches due to the inherently non-linear behavior of a coupled cluster wavefunction representation, we propose new approaches based on an intuitive, well-defined condition for sampling weights and on sampling the expansion in cluster operators of different excitation levels. We term these modifications even and truncated selections, respectively. Utilising both approaches demonstrates dramatically improved calculation stability as well as reduced computational and memory costs. These modifications are particularly effective at higher truncation levels owing to the large number of terms within the cluster expansion that can be neglected, as demonstrated by the reduction of the number of terms to be sampled when truncating at triple excitations by 77% and hextuple excitations by 98%.
我们考虑在随机耦合簇理论中对耦合簇展开进行抽样。观察到由于耦合簇波函数表示的固有非线性行为，先前方法存在局限性，我们提出了新的方法，这些方法基于抽样权重的直观、明确定义的条件，以及对不同激发水平的簇算符展开进行抽样。我们分别将这些修改称为均匀抽样和截断抽样。利用这两种方法可以显著提高计算稳定性，同时降低计算和存储成本。由于在簇展开中有大量可以忽略的项，因此这些修改在更高的截断水平下特别有效，例如在三重激发截断时抽样项数减少了 77%，在六重激发截断时抽样项数减少了 98%。
