论文标题
量化和减少代数示意构造理论的自旋污染的电荷激发理论
Quantifying and reducing spin contamination in algebraic diagrammatic construction theory of charged excitations
论文作者
论文摘要
代数图解结构（ADC）理论是一种用于模拟化学系统中电子激发的计算高效且准确的方法。但是，对于具有未配对电子的分子中激发态的模拟，ADC方法的性能可能会受到无限制的Hartree-Fock（UHF）参考波函数中的自旋污染的影响。在这项工作中，我们基于用UHF参考轨道（EA/IP-ADC/UHF）进行电子附着和开放壳分子电离的ADC方法的准确性，并开发了一种方法来量化带电激发态的自旋污染。经过此评估后，我们证明可以通过将EA/IP-ADC与受限制的开放式shell Hartree-Fock（ROHF）或轨道优化的Møller-Plesset扰动（OMP）理论相结合的参考轨道来减少自旋污染。我们的数值结果表明，对于在UHF参考中具有强旋转污染的开放式系统，具有ROHF或OMP参考轨道的三阶EA/IP-ADC方法的准确性与具有单一和双重激发的运动耦合群集理论相似。
Algebraic diagrammatic construction (ADC) theory is a computationally efficient and accurate approach for simulating electronic excitations in chemical systems. However, for the simulations of excited states in molecules with unpaired electrons the performance of ADC methods can be affected by the spin contamination in unrestricted Hartree-Fock (UHF) reference wavefunctions. In this work, we benchmark the accuracy of ADC methods for electron attachment and ionization of open-shell molecules with the UHF reference orbitals (EA/IP-ADC/UHF) and develop an approach to quantify the spin contamination in the charged excited states. Following this assessment, we demonstrate that the spin contamination can be reduced by combining EA/IP-ADC with the reference orbitals from restricted open-shell Hartree-Fock (ROHF) or orbital-optimized Møller-Plesset perturbation (OMP) theories. Our numerical results demonstrate that for open-shell systems with strong spin contamination in the UHF reference the third-order EA/IP-ADC methods with the ROHF or OMP reference orbitals are similar in accuracy to equation-of-motion coupled cluster theory with single and double excitations.
