Equation-of-Motion Coupled-Cluster Theory to Model L-Edge X-ray Absorption and Photoelectron Spectra

Abstract

We present an extension of the equation-of-motion coupled-cluster singles and doubles (EOM-CCSD) theory for computing x-ray Ledge spectra, both in the absorption (XAS) and photoelectron (XPS) regimes. The approach is based on the perturbative evaluation of spin-orbit couplings using the Breit-Pauli Hamiltonian and nonrelativistic wave-functions described by the fc-CVS-EOM-CCSD ansatz (EOM-CCSD within the frozen-core core-valence separated (fc-CVS) scheme). The formalism is based on spinless one-particle density matrices. The approach is illustrated by modeling XAS and XPS of several model systems ranging from argon atoms to small molecules containing sulfur and silicon. File list (2) download file view on ChemRxiv Ledges .pdf (1.93 MiB) download file view on ChemRxiv L-edges_SI.pdf (259.57 KiB)

The nuts and bolts of core-hole constrained ab initio simulation for K-shell x-ray photoemission and absorption spectra

“…Using these approximations to obtain intensities and line shapes, the problem of simulating XPS spectra is reduced to finding the binding energies E B of the relevant electronic core-states. Ab initio calculation of core-level binding energies: many different approaches exist to calculate core-level binding energies including CC [49], equation-of-motion CC (EOM-CC) [20], the GW method [16,17], and real-time TD-DFT [50]. The simplest approach, however, is the use of Koopmans' theorem (2.5), which relates the ionization potential of an electronic state in Hartree-Fock theory with the negative of the relevant Hartree-Fock eigenstate [51].…”

Relativistic coupled‐cluster and equation‐of‐motion coupled‐cluster methods

“…The core‐valence separation (CVS) 280 scheme has recently been adapted to the EOM‐CCSD method 281 to avoid the convergence problem due to the coupling between core‐ionized states and high‐lying valence continuum states. CVS‐EOM‐CCSD calculations of L‐edge spectra for third‐row elements with perturbative treatment of spin‐orbit coupling has recently been reported 282 . Meanwhile, the CVS‐EOM‐CC methods with non‐perturbative treatment of spin‐orbit coupling can further extend the applicability to calculations of L‐edge spectra for heavy elements.…”

Probing Molecular Chirality of Ground and Electronically Excited States in the UV-vis and X-ray Regimes: An EOM-CCSD Study

“…We implemented the above expressions for the calculation of the electronic circular dichroism within the EOM-CCSD approach in Q-Chem. 64,65 The theory is applicable for valence excitations (EOMEE-CCSD) and well as core excitations (fc-CVS-EOMEE-CCSD 32,66 ) of both ground and excited states. py-CCRSP 67 was used for code profiling and testing and for the CPP calculations.…”

“…77, we considered the chlorine L-edge of chloroethanol. XAS and XCD spectra with and without spin-orbit coupling (SOC) were computed with the 6-311(2+,+)G** basis uncontracted to describe the 2p orbitals of the Cl atom 66. Unless otherwise specified, the gauge origin was located at the center of charge (coc), which is the default setup in Q-Chem.…”