Nanda Kaushik D, Vidal Marta L, Faber Rasmus, Coriani Sonia, Krylov Anna I
Department of Chemistry, University of Southern California, Los Angeles, California 90089, USA.
DTU Chemistry - Department of Chemistry, Technical University of Denmark, DK-2800, Kongens Lyngby, Denmark.
Phys Chem Chem Phys. 2020 Feb 7;22(5):2629-2641. doi: 10.1039/c9cp03688a. Epub 2019 Oct 10.
We present a novel approach for computing resonant inelastic X-ray scattering (RIXS) cross sections within the equation-of-motion coupled-cluster (EOM-CC) framework. The approach is based on recasting the sum-over-states expressions for RIXS moments into closed-form expressions by using damped response theory. Damped response formalism allows one to circumvent problems of divergent behavior of response equations in the resonant regime. However, the convergence of response equations in the X-ray frequency range is often erratic due to the electronically metastable (i.e., resonant) nature of the virtual core-excited states embedded in the valence ionization continuum. We circumvent this problematic behavior by extending the core-valence separation (CVS) scheme, which decouples the valence-excited and core-excited configurations of the excitation manifold, into the response domain. The accuracy of the CVS-enabled damped response theory, implemented within the EOM-EE-CCSD (EOM-CC for excitation energies with single and double excitations) framework, is assessed by comparison against standard damped EOM-EE-CCSD response calculations. The capabilities of the new approach are illustrated by calculations of RIXS cross sections for benzene and benzene radical cation.
我们提出了一种在运动方程耦合簇（EOM-CC）框架内计算共振非弹性X射线散射（RIXS）截面的新方法。该方法基于通过使用阻尼响应理论将RIXS矩的态求和表达式重铸为封闭形式的表达式。阻尼响应形式主义使人们能够规避共振区域中响应方程发散行为的问题。然而，由于嵌入价电离连续体中的虚拟芯激发态的电子亚稳（即共振）性质，X射线频率范围内响应方程的收敛通常不稳定。我们通过将核心-价分离（CVS）方案扩展到响应域来规避这种有问题的行为，该方案将激发流形的价激发和芯激发构型解耦。在EOM-EE-CCSD（用于单激发和双激发的激发能的EOM-CC）框架内实现的启用CVS的阻尼响应理论的准确性，通过与标准阻尼EOM-EE-CCSD响应计算进行比较来评估。通过计算苯和苯自由基阳离子的RIXS截面来说明新方法的能力。
