Masios Nikolaos, Hummel Felix, Grüneis Andreas, Irmler Andreas
Institute for Theoretical Physics, TU Wien, Wiedner Hauptstraße 8-10/136, 1040 Vienna, Austria.
J Chem Theory Comput. 2024 Jul 23;20(14):5937-5950. doi: 10.1021/acs.jctc.4c00224. Epub 2024 Jul 8.
We investigate the convergence of coupled-cluster (CC) correlation energies and related quantities with respect to the employed basis set size for the uniform electron gas (UEG) to gain a better understanding of the basis set incompleteness error (BSIE). To this end, coupled-cluster doubles (CCD) theory is applied to the three-dimensional UEG for a range of densities, basis set sizes, and electron numbers. We present a detailed analysis of individual diagrammatically decomposed contributions to the amplitudes at the level of CCD theory. In particular, we show that only two terms from the amplitude equations contribute to the asymptotic large-momentum behavior of the transition structure factor, corresponding to the cusp region at short interelectronic distances. However, due to the coupling present in the amplitude equations, all decomposed correlation energy contributions show the same asymptotic convergence behavior to the complete basis set limit. These findings provide an additional rationale for the success of a recently proposed correction to the BSIE of CC theory. Lastly, we examine the BSIE in the CCD plus perturbative triples [CCD(T)] method, as well as in the newly proposed CCD plus complete perturbative triples [CCD(cT)] method.
我们研究了耦合簇（CC）相关能及相关量对于均匀电子气（UEG）所采用基组大小的收敛性，以更好地理解基组不完备误差（BSIE）。为此，将耦合簇双激发（CCD）理论应用于三维UEG，涵盖一系列密度、基组大小和电子数。我们在CCD理论层面详细分析了对振幅的各个图解分解贡献。特别地，我们表明振幅方程中只有两项对跃迁结构因子的渐近大动量行为有贡献，这对应于短电子间距处的尖点区域。然而，由于振幅方程中存在耦合，所有分解的相关能贡献在向完全基组极限收敛时表现出相同的渐近收敛行为。这些发现为最近提出的对CC理论BSIE的修正的成功提供了额外的理论依据。最后，我们研究了CCD加微扰三重激发[CCD(T)]方法以及新提出的CCD加完全微扰三重激发[CCD(cT)]方法中的BSIE。
