论文标题
评估轨道优化的统一ANSATZ的密度累积理论
Assessing the Orbital-Optimized Unitary Ansatz for Density Cumulant Theory
论文作者
论文摘要
先前提议的ANSATZ用于密度累积理论，该理论结合了轨道优化和根据单一耦合簇幅度（OUDCT）而对2电子降低密度矩阵累积的参数化。正式地，我们阐明了OUDCT和轨道优化的统一耦合群集理论之间的关系，并显示了准确的和某些近似OUDCT方法的平稳性条件中接近零分母的存在。我们实施了OUDCT ANSATZ的方法，仅限于数值研究的双重激励，直到贝克兼兼贝克贝尔 - 霍斯多夫（Baker-Campbell-Hausdorff）扩展中的第五个换向器。我们发现，超出先前已知的ODC-12方法的ANSATZ的方法对于平衡属性的准确性降低，并且在尝试描述$ H2 $解离时较不可能。需要新的发展来制定更准确的DCT变体。
The previously proposed ansatz for density cumulant theory that combines orbital-optimization and a parameterization of the 2-electron reduced density matrix cumulant in terms of unitary coupled cluster amplitudes (OUDCT) is carefully examined. Formally, we elucidate the relationship between OUDCT and orbital-optimized unitary coupled cluster theory and show the existence of near-zero denominators in the stationarity conditions for both the exact and some approximate OUDCT methods. We implement methods of the OUDCT ansatz restricted to double excitations for numerical study, up to the fifth commutator in the Baker-Campbell-Hausdorff expansion. We find that methods derived from the ansatz beyond the previously known ODC-12 method tend to be less accurate for equilibrium properties and less reliable when attempting to describe $H2$ dissociation. New developments are needed to formulate more accurate DCT variants.
