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arXiv 2103.06180cond-mat.mtrl-sciphysics.chem-ph
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大基组下金属动力学相关能的下折叠和合成方法

Dynamical correlation energy of metals in large basis sets from downfolding and composite approaches

James M. Callahan, Malte F. Lange, Timothy C. Berkelbach

摘要:

单双激发耦合团簇理论(CCSD)是一种很有前途的三维金属电子结构的从头计算方法,但二阶微扰理论(MP2)在热力学极限上存在分歧。然而,由于成本高,收敛性差的CCSD的基规模方面,CCSD应用于周期系统往往会导致大的基集误差。在一个常见的“复合”方法中,MP2被用来通过焦点校正来恢复丢失的动力学相关能,但MP2对金属的不足引起了人们对这种方法的质疑。在这里,我们描述了如何处理MP2的高能量激发可以“向下折叠”到一个低能量的活动空间CCSD治疗。比较复合和向下折叠的方法如何执行均匀的电子气,我们发现,后者收敛更快的基组大小。尽管如此,复合方法是令人惊讶的准确,因为它消除了有问题的MP2处理费米表面附近的双激发。用该方法在完全基组和热力学极限下估计CCSD的相关能,发现CCSD在$r_s=4$上恢复了90%以上的精确相关能。我们还测试了复合材料和向下折叠的方法与随机相位近似代替MP2,产生一种更有效,但更昂贵的方法。

英文摘要:

Coupled-cluster theory with single and double excitations (CCSD) is a promising ab initio method for the electronic structure of three-dimensional metals, for which second-order perturbation theory (MP2) diverges in the thermodynamic limit. However, due to the high cost and poor convergence of CCSD with respect to basis size, applying CCSD to periodic systems often leads to large basis set errors. In a common "composite" method, MP2 is used to recover the missing dynamical correlation energy through a focal-point correction, but the inadequacy of MP2 for metals raises questions about this approach. Here we describe how high-energy excitations treated by MP2 can be "downfolded" into a low-energy active space to be treated by CCSD. Comparing how the composite and downfolding approaches perform for the uniform electron gas, we find that the latter converges more quickly with respect to the basis set size. Nonetheless, the composite approach is surprisingly accurate because it removes the problematic MP2 treatment of double excitations near the Fermi surface. Using the method to estimate the CCSD correlation energy in the combined complete basis set and thermodynamic limits, we find CCSD recovers over 90% of the exact correlation energy at $r_s=4$. We also test the composite and downfolding approaches with the random-phase approximation used in place of MP2, yielding a method that is more effective but more expensive.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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