基于价键理论的耦合簇方法研究

The proposal of this project is to develop valence bond (VB) coupled-cluster (CC) theory, including method and program developments. The theoretical and methodological developments include: 1) the extension of enhanced Wick’s theorem to the cases of unitary generator and commutator; 2) and the development of automatic formula/code generator (AFCG) based on it; 3) internally contracted VB unitary CC (icVBUCC) theory and its perturbative approximation (icVBUCCPT), and further development and efficient implementation of their molecular orbital theory correspondences icMRUCC and icMRUCCPT. The successful development of icVBUCC and icVBUCCPT will provide methods which simultaneously exhibit the conceptual lucidity and the accurate results which can be provided by VB and CC theories, respectively. Thus extend the research field of VB theory to the accurate calculations of complicated chemical systems. Moreover, the newly developed AFCG will become a useful tool for developing novel methods and algorithms in spin-free quantum chemistry.

本项目将开展基于价键理论的耦合簇方法，特别是价键酉耦合簇方法的理论研究、程序开发和应用研究，包括Enhanced Wick定理在酉生成子和对易子情形下的推广，基于这个定理的自动公式/代码生成器开发，内收缩价键酉耦合簇方法（icVBUCC）和其微扰近似方法（icVBUCCPT）方法和程序的开发以及相应分子轨道方法icMRUCC和icMRUCCPT的进一步发展和高效程序实现。项目拟发展的自动公式/代码生成器研发将为量子化学计算方法研究者提供有益工具。项目拟开展的方法研究成果将结合价键理论化学图像清晰易于定性解释化学现象和耦合簇方法计算精度高、结果可靠的优势，从而将价键理论的应用研究领域拓展到复杂体系的高精度量子化学计算。

本项目自2015年实施以来，根据研究计划开展从头算价键理论新方法和新算法研究，提出了基于Seniority数的价键计算方法和算法，发展了Cholesky分解技术在大体系价键计算中的应用，开展的方法和算法研究成果进一步发展了从头算价键理论方法，实现了上述方法和算法的程序化，进而颁布了功能更加丰富更加强大的更新版本XMVB程序包，并应用项目发展的方法、算法和程序开展了一系列化学键本质问题的价键理论计算研究。本项目发表了5篇相关学术论文。