Variational quantum eigensolver simulations with the multireference unitary coupled cluster ansatz: a case study of the <i>C</i><sub>2<i>v</i></sub> quasi-reaction pathway of beryllium insertion into a H<sub>2</sub> molecule
Variational quantum eigensolver simulations with the multireference unitary coupled cluster ansatz: a case study of the <i>C</i><sub>2<i>v</i></sub> quasi-reaction pathway of beryllium insertion into a H<sub>2</sub> molecule
复制标题
多参考酉耦合簇 ansatz 的变分量子本征解算器模拟：铍插入 a 中的 <i>C</i><sub>2<i>v</i></sub> 准反应途径的案例研究
DOI：
10.1039/d1cp04318h
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发表时间：
2022
影响因子：
3.3
通讯作者：
Mochizuki Yuji
中科院分区：
文献类型：
--
作者：
Sugisaki Kenji;Kato Takumi;Minato Yuichiro;Okuwaki Koji;Mochizuki Yuji
变分量子本征解算器（VQE）为基础的量子化学计算已被广泛研究，作为一种计算模型，使用嘈杂的中等规模的量子器件。VQE使用一个通过“Anantrons”定义的参数化量子电路来产生近似的波函数，而Anantrons的适当选择是最重要的一步。由于大多数化学问题都集中在两个电子状态或结构之间的能量差异上，因此以相同的精度计算不同分子结构中的总能量对于正确理解化学和化学过程至关重要。在这种背景下，发展能够准确描述强关联系统电子结构的ansatzes是一项重要的任务。在这里，我们应用了一个传统的单一耦合集群（UCC）和一个新开发的多参考单一耦合集群与部分广义的单打和双打（MR-UCCpGSD）ansatzes的准反应途径的Be插入到H2，LiH分子下共价键解离，和一个矩形的四氢集群被称为P4集群，这些都是代表性的系统中，静态电子相关效应是突出的。我们的数值模拟表明，UCCSD模型在Be + H2 → BeH 2反应路径中发生避免交叉的点附近表现出非常缓慢的收敛行为，导致模拟的VQE能量与全组态相互作用（full-CI）值有很大的差异。相比之下，MR-UCCpGSD模型在总能量和与全CI解的重叠方面可以给出更可靠的结果，坚持了多构型处理在强关联系统计算中的重要性。MR-UCCpGSD模型使我们能够以相同的精度计算能量，而不管多构型特征的强度如何，这是讨论各种分子系统能量差异的基本性质。
Variational quantum eigensolver (VQE)-based quantum chemical calculations have been extensively studied as a computational model using noisy intermediate-scale quantum devices. The VQE uses a parametrized quantum circuit defined through an “ansatz” to generate approximated wave functions, and the appropriate choice of an ansatz is the most important step. Because most chemistry problems focus on the energy difference between two electronic states or structures, calculating the total energies in different molecular structures with the same accuracy is essential to correctly understand chemistry and chemical processes. In this context, the development of ansatzes that are capable of describing electronic structures of strongly correlated systems accurately is an important task. Here we applied a conventional unitary coupled cluster (UCC) and a newly developed multireference unitary coupled cluster with partially generalized singles and doubles (MR-UCCpGSD) ansatzes to the quasi-reaction pathway of Be insertion into H2, LiH molecule under covalent bond dissociation, and a rectangular tetra-hydrogen cluster known as a P4 cluster; these are representative systems in which the static electron correlation effect is prominent. Our numerical simulations revealed that the UCCSD ansatz exhibits extremely slow convergence behaviour around the point where an avoided crossing occurs in the Be + H2 → BeH2 reaction pathway, resulting in a large discrepancy of the simulated VQE energy from the full-configuration interaction (full-CI) value. By contrast, the MR-UCCpGSD ansatz can give more reliable results with respect to total energy and the overlap with the full-CI solution, insisting the importance of multiconfigurational treatments in the calculations of strongly correlated systems. The MR-UCCpGSD ansatz allows us to compute the energy with the same accuracy regardless of the strength of multiconfigurational character, which is an essential property to discuss energy differences of various molecular systems.