2DM的变分优化：使用扩展的聚类约束逼近三指标精度
Variational optimization of the 2DM: approaching three-index accuracy using extended cluster constraints
摘要：
对二维哈伯德模型的简化密度矩阵进行变分优化。利用系统中存在的所有对称性，我们已经能够研究$6\times6$晶格在不同的填充和不同的值的现场排斥，使用高精度，但计算昂贵的三指数条件。为了减少计算成本，我们研究了施加三个索引约束的本地集群的$2\times2$和$3\times3$网站的性能。随后，我们得到新的限制，扩展这些集群的限制，将一个更大的晶格上的集群的开放系统的性质。通过对$6\times6$格进行原理证明计算，证明了实现这些新约束的可行性。结果表明，大部分的三个索引的结果可以恢复使用这些扩展的集群约束，在一小部分的计算成本。
英文摘要：
The reduced density matrix is variationally optimized for the two-dimensional Hubbard model. Exploiting all symmetries present in the system, we have been able to study $6\times6$ lattices at various fillings and different values for the on-site repulsion, using the highly accurate but computationally expensive three-index conditions. To reduce the computational cost we study the performance of imposing the three-index constraints on local clusters of $2\times2$ and $3\times3$ sites. We subsequently derive new constraints which extend these cluster constraints to incorporate the open-system nature of a cluster on a larger lattice. The feasibility of implementing these new constraints is demonstrated by performing a proof-of-principle calculation on the $6\times6$ lattice. It is shown that a large portion of the three-index result can be recovered using these extended cluster constraints, at a fraction of the computational cost.
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