带电激发的扩展二阶多参考代数图构造理论
Extended Second-Order Multireference Algebraic Diagrammatic Construction Theory for Charged Excitations
摘要：
我们报告了一个新的实现多参考代数图解构造理论（MR-ADC）的电子附着和电离的强关联分子系统（EA/IP-MR-ADC）的模拟。根据我们最近关于IP-MR-ADC的工作[J. Chem. 2019，15，5908]，我们提出了用于电子附着的二阶MR-ADC方法（EA-MR-ADC（2））的第一个实现，以及两个扩展的二阶近似（EA-和IP-MR-ADC（2）-X），其中包含三阶电子相关效应的部分处理。引入有效哈密顿量的二阶振幅的小近似，我们的EA-和IP-MR-ADC（2）-X的实现具有低O（M^5）的计算缩放，基组大小为M。此外，我们描述了一个有效的算法，用于解决一阶振幅方程的MR-ADC和部分收缩的二阶N-电子价微扰理论（NEVPT 2），完全避免了计算的四粒子约化密度矩阵，而不引入任何近似或瞬时传播。对于八个小分子、碳二聚体和扭曲乙烯的基准组，我们证明了EA-和IP-MR-ADC（2）-X实现了与强收缩NEVPT 2相似的精度，同时具有较低的计算缩放活性空间大小，并提供了有效的过渡特性。
英文摘要：
We report a new implementation of multireference algebraic diagrammatic construction theory (MR-ADC) for simulations of electron attachment and ionization in strongly correlated molecular systems (EA/IP-MR-ADC). Following our recent work on IP-MR-ADC [J. Chem. Theory Comput. 2019, 15, 5908], we present the first implementation of the second-order MR-ADC method for electron attachment (EA-MR-ADC(2)), as well as two extended second-order approximations (EA- and IP-MR-ADC(2)-X) that incorporate a partial treatment of third-order electron correlation effects. Introducing a small approximation for the second-order amplitudes of the effective Hamiltonian, our implementation of EA- and IP-MR-ADC(2)-X has a low O(M^5) computational scaling with the basis set size M. Additionally, we describe an efficient algorithm for solving the first-order amplitude equations in MR-ADC and partially-contracted second-order N-electron valence perturbation theory (NEVPT2) that completely avoids computation of the four-particle reduced density matrices without introducing any approximations or imaginary-time propagation. For a benchmark set of eight small molecules, carbon dimer, and a twisted ethylene, we demonstrate that EA- and IP-MR-ADC(2)-X achieve accuracy similar to that of strongly-contracted NEVPT2, while having a lower computational scaling with the active space size and providing efficient access to transition properties.
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