In this work we demonstrate that the heat bath configuration interaction (HCI) and its semistochastic extension can be used to treat relativistic effects and electron correlation on an equal footing in large active spaces to calculate the low energy spectrum of several systems including halogen group atoms (F, Cl, Br, I), coinage atoms (Cu, Au), and the neptunyl(VI) dioxide radical. This work demonstrates that despite a significant increase in the size of the Hilbert space due to spin symmetry breaking by the spin–orbit coupling terms, HCI retains the ability to discard large parts of the low importance Hilbert space to deliver converged absolute and relative energies. For instance, by using just over 10⁷ determinants we get converged excitation energies for Au atom in an active space containing (150o,25e) which has over 10³⁰ determinants. We also investigate the accuracy of five different two-component relativistic Hamiltonians in which different levels of approximations are made in deriving the one-electron and two-electrons Hamiltonians, ranging from Breit–Pauli (BP) to various flavors of exact two-component (X2C) theory. The relative accuracy of the different Hamiltonians are compared on systems that range in atomic number from first row atoms to actinides.

中文翻译：

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大型活动空间中自旋轨道耦合和电子相关性的一步式处理

在这项工作中，我们证明了热浴构型相互作用（HCI）及其半随机扩展可用于在较大的活动空间中以相等的基础来处理相对论效应和电子相关性，以计算包括卤素基团原子在内的多个系统的低能谱（ F，Cl，Br，I），造币原子（Cu，Au）和Neptunyl（VI）二氧自由基。这项工作表明，尽管由于自旋轨道耦合项的自旋对称性破坏而使希尔伯特空间的大小显着增加，但HCI仍保留了丢弃大部分低重要性希尔伯特空间以传递会聚绝对和相对能量的能力。例如，使用超过10 ⁷行列式我们在包含（150o，25e）的活动空间中获得了10个^30以上行列式的Au原子的会聚激发能。我们还研究了五种不同的两成分相对论哈密顿量的准确性，其中在推导一电子和两电子哈密顿量时采用了不同程度的近似值，范围从Breit–Pauli（BP）到各种口味的精确的两成分（ X2C）理论。在从第一行原子到act系元素的原子序数范围内的系统上，比较了不同哈密顿量的相对精度。