从任意参考子空间逼近全组态相互作用低能谱
Approaching the Full Configuration Interaction Low-Energy Spectrum from an Arbitrary Reference Subspace
摘要：
在以前的工作（arXiv：2010.02027）中，我们展示了如何通过梯度下降或拟牛顿算法获得全组态相互作用（FCI）基态能量作为任意参考波函数的函数。在这里，我们扩展这种方法，并考虑从任意参考子空间的哈密顿量的低能量子空间的优化。沿优化路径的能量得到的参考子空间中的状态之间的过渡矩阵元素。我们展示了一个应用程序的算法与参考子空间构造的非正交配置相互作用（NOCI）形式主义来描述避免交叉LiF和低洼的单重态和三重态光谱的甲醛。
英文摘要：
In a previous work (arXiv:2010.02027) we showed how the full configuration interaction (FCI) ground state energy can be obtained as a functional of an arbitrary reference wavefunction by means of a gradient descent or quasi-Newton algorithm. Here, we extend this approach and consider the optimization of the low-energy subspace of the Hamiltonian from an arbitrary reference subspace. The energies along the optimization path are obtained in terms of transition matrix elements among the states in the reference subspace. We show an application of the algorithm with a reference subspace constructed from a non-orthogonal configuration interaction (NOCI) formalism to describe the avoided crossing in LiF and the low-lying singlet and triplet spectrum of formaldehyde.
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