Hodecker Manuel, Dempwolff Adrian L, Schirmer Jochen, Dreuw Andreas
Interdisciplinary Center for Scientific Computing, Heidelberg University, Im Neuenheimer Feld 205, 69120 Heidelberg, Germany.
Theoretical Chemistry, Heidelberg University, Im Neuenheimer Feld 229, 69120 Heidelberg, Germany.
J Chem Phys. 2022 Feb 21;156(7):074104. doi: 10.1063/5.0070967.
This article describes a novel approach for the calculation of ionization potentials (IPs), or, more generally, electron-detachment energies, based on a unitary coupled-cluster (UCC) parameterization of the ground-state wave function. Explicit working equations for a scheme referred to as IP-UCC3 are given, providing electron-detachment energies and spectroscopic amplitudes of electron-detached states dominated by one-hole excitations correct through third order. In the derivation, an expansion of the UCC transformed Hamiltonian involving Bernoulli numbers as expansion coefficients is employed. Both the secular matrix and the effective transition moments are shown to be essentially equivalent to the strict third-order algebraic-diagrammatic construction scheme for the electron propagator (IP-ADC). Interestingly, due to the Bernoulli expansion, neglecting triple substitutions in the UCC expansion manifold does not affect the third-order consistency of the IP-UCC effective transition moments. Finally, the equivalence between ADC and UCC excited-state schemes is shown to not hold in fourth or higher order due to a different treatment of the correlated excited-state basis.
本文描述了一种基于基态波函数的酉耦合簇（UCC）参数化来计算电离势（IP），或者更一般地说，电子脱离能的新方法。给出了一种称为IP-UCC3的方案的显式工作方程，提供了由单空穴激发主导的电子脱离态的电子脱离能和光谱振幅，精确到三阶。在推导过程中，采用了以伯努利数作为展开系数的UCC变换哈密顿量的展开式。久期矩阵和有效跃迁矩都被证明与电子传播子的严格三阶代数图示构造方案（IP-ADC）基本等效。有趣的是，由于伯努利展开，在UCC展开流形中忽略三重替换不会影响IP-UCC有效跃迁矩的三阶一致性。最后，由于对相关激发态基的不同处理，ADC和UCC激发态方案之间的等效性在四阶或更高阶不成立。
