论文标题
统一耦合群集能量景观的新当地探索
New Local Explorations of the Unitary Coupled Cluster Energy Landscape
论文作者
论文摘要
最近的量子信息繁荣影响了统一耦合簇（UCC）理论的兴趣复兴。我们小组对统一Ansätze的局部能源景观的兴趣促使我们调查了二阶截断UCCSD Energy的Taylor系列扩展（而不是扰动扩张）的经典方法。这等于一种方法，即通过从Hartree-Fock到UCCSD的单个牛顿 - 拉夫森步骤来估算电子相关能量。以前曾探索过这种方法，但是准确性没有得到广泛的研究。在本文中，我们研究了性能，并观察到与单打和双打线性化耦合簇相似的病理。我们介绍了三个或更高订单的衍生物的使用，以帮助部分恢复真实UCCSD的变异下限，从而将这些衍生物限制为“未混合”类别的衍生物，以简化模型。通过测试几个势能表面和反应能的方法，我们发现这种“对角线”近似对高阶项有效，可有效地降低近乎奇异性的敏感性，以实现密切相关的状态，同时却没有显着降低弱相关系统的准确性。
The recent quantum information boom has effected a resurgence of interest in unitary coupled cluster (UCC) theory. Our group's interest in local energy landscapes of unitary ansätze prompted us to investigate the classical approach of truncating the Taylor series expansion (instead of a perturbative expansion) of UCCSD energy at second-order. This amounts to an approach where electron correlation energy is estimated by taking a single Newton-Raphson step from Hartree-Fock toward UCCSD. Such an approach has been explored previously, but the accuracy was not extensively studied. In this paper, we investigate the performance and observe similar pathologies to linearized coupled cluster with singles and doubles. We introduce the use of derivatives of order three or greater to help partially recover the variational lower bound of true UCCSD, restricting these derivatives to those of the "unmixed" category in order to simplify the model. By testing the approach on several potential energy surfaces and reaction energies, we find this "diagonal" approximation to higher order terms to be effective at reducing sensitivity near singularities for strongly correlated regimes, while not significantly diminishing the accuracy of weakly correlated systems.
