Quantifying the error of the core-valence separation approximation

Abstract

For the calculation of core-excited states probed through X-ray absorption spectroscopy, the core-valence separation (CVS) scheme has become a vital tool. This approach allows to target such states with high specificity, albeit introducing an error. We report the implementation of a post-processing step for CVS excitations obtained within the algebraic-diagrammatic construction scheme for the polarisation propagator (ADC), which removes this error. Based on this we provide a detailed analysis of the CVS scheme, identifying its accuracy to be dominated by an error balance between two neglected couplings, one between core and valence single excitations and one between single and double core excitations. The selection of the basis set is shown to be vital for a proper description of both couplings, with tight polarising functions being necessary for a good balance of errors. The CVS error is confirmed to be stable across multiple systems, with an element-specific spread for $K$-edge spectrum calculations of about $\pm$0.02 eV. A systematic lowering of the CVS error by 0.02-0.03 eV is noted when considering excitations to extremely diffuse states, emulating ionisation.

References in corpus (3)

• adcc: A versatile toolkit for rapid development of algebraic-diagrammatic construction methods
• Third-order algebraic diagrammatic construction theory for electron attachment and ionization energies: Conventional and Green's function implementation
• Simulating X-ray absorption spectra with linear-response density cumulant theory

Cited by in corpus (9)

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• Core Excitations with Excited State Mean Field and Perturbation Theory
• Algebraic Diagrammatic Construction Theory for Simulating Charged Excited States and Photoelectron Spectra
• Simulating Transient X-ray Photoelectron Spectra of Fe(CO)5 and Its Photodissociation Products With Multireference Algebraic Diagrammatic Construction Theory
• Self-Adaptive Real-Time Time-Dependent Density Functional Theory for X-ray Absorptions
• Resonant Double-Core Excitations with Ultrafast, Intense Pulses
• Core-Ionized States and X-ray Photoelectron Spectra of Solids From Periodic Algebraic Diagrammatic Construction Theory