Generalized single excitation configuration interaction: an investigation into the impact of the inclusion of non-orthogonality on the calculation of core-excited states

Oosterbaan, Katherine J.; White, Alec F.; Hait, Diptarka; Head‐Gordon, Martin

doi:10.1039/c9cp06592j

Cited by 28 publications

(35 citation statements)

References 69 publications

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“…A comprehensive review of X-ray absorption simulation techniques has been published recently by Norman and Dreuw. [6] Briefly, one possible choice is to use wave function based methods like coupled-cluster (CC), [7][8][9][10][11][12][13][14] symmetry adapted clusterconfiguration interaction (SAC-CI), [15,16] configuration interaction, [17][18][19][20][21][22] or the algebraic-diagramatic construction (ADC) method. [23][24][25][26][27][28] In general, all of these methods are accurate and reliable.…”

Section: Introductionmentioning

confidence: 99%

PSIXAS: A Psi4 plugin for efficient simulations of X‐ray absorption spectra based on the transition‐potential and Δ‐Kohn–Sham method

Ehlert

Klamroth

2020

J Comput Chem

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Near edge X‐ray absorption fine structure (NEXAFS) spectra and their pump‐probe extension (PP‐NEXAFS) offer insights into valence‐ and core‐excited states. We present PSIXAS, a recent implementation for simulating NEXAFS and PP‐NEXAFS spectra by means of the transition‐potential and the Δ‐Kohn–Sham method. The approach is implemented in form of a software plugin for the Psi4 code, which provides access to a wide selection of basis sets as well as density functionals. We briefly outline the theoretical foundation and the key aspects of the plugin. Then, we use the plugin to simulate PP‐NEXAFS spectra of thymine, a system already investigated by others and us. It is found that larger, extended basis sets are needed to obtain more accurate absolute resonance positions. We further demonstrate that, in contrast to ordinary NEXAFS simulations, where the choice of the density functional plays a minor role for the shape of the spectrum, for PP‐NEXAFS simulations the choice of the density functional is important. Especially hybrid functionals (which could not be used straightforwardly before to simulate PP‐NEXAFS spectra) and their amount of “Hartree‐Fock like” exact exchange affects relative resonance positions in the spectrum.

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Section: Introductionmentioning

confidence: 99%

PSIXAS: A Psi4 plugin for efficient simulations of X‐ray absorption spectra based on the transition‐potential and Δ‐Kohn–Sham method

Ehlert

Klamroth

2020

J Comput Chem

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“…This observation would suggest that the model with localized holes states for a system with symmetry equivalent atoms provides the best zeroth-order picture for core ionization in these systems. The approach proposed here for core photoionization calculations is related to the one-center non-orthogonal configuration interaction with single substitutions (1C-NOCIS) method which has been proposed for the study of metastable core-excited states [30]. In the NOCIS method non-orthogonal configurations based on localized orbitals provide a superior reference basis in which to describe electron correlation in an isolated molecule, while here such configurations provide a better reference from which to describe channel coupling in the presence of the photoelectron, which is also an electron correlation effect.…”

Section: Discussionmentioning

confidence: 99%

Validity of the static-exchange approximation for inner-shell photoionization of polyatomic molecules

et al. 2020

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The simple single-channel static-exchange approximation completely ignores correlation between the continuum and molecular ion electrons. In molecular systems with symmetry equivalent atoms, the single-channel approximation can seriously fail in core ionization when using delocalized orbitals to represent the core hole states. We present cross sections and molecular frame photoelectron angular distributions with both localized and delocalized core orbitals in CF4 F (1s) ionization. We show that only a full coupled-channel calculation can recover an accurate description of the physics of inner-shell photoionization when using delocalized orbitals, whereas nearly the same result can be obtained from independent single-channel static-exchange calculations when localized core orbitals are used. A grid-based variational method described here makes such single-channel calculations possible on larger systems without local-exchange approximations. Illustrative calculations on the core ionization of SF6 are presented to illustrate the power of the grid-based method.

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“…Typically, a fractional occupancy of 0.5 is used which is suitable for core‐excitations since it provides a balance between initial and final state effects 85 . Another method that goes beyond the STEX approximation through the inclusion of the coupling between non‐orthogonal configurations is non‐orthogonal configuration interaction singles (NOCIS) 86,87 . Prendergast and co‐workers have developed the excited electron and core‐hole approach (XCH) which models the first core‐excited state by representing the core‐excited atom using a modified pseudopotential, and the electron excited from this atom is placed in the first available valence orbital 88‐91 .…”

Section: X‐ray Absorption Spectroscopymentioning

confidence: 99%

Modeling of the spectroscopy of core electrons with density functional theory

Besley

2021

WIREs Comput Mol Sci

100

104

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The availability of X‐ray light sources with increased resolution and intensity has provided a foundation for increasingly sophisticated experimental studies exploiting the spectroscopy of core electrons to probe fundamental chemical, physical, and biological processes. Quantum chemical calculations can play a critical role in the analysis of these experimental measurements. The relatively low computational cost of density functional theory (DFT) and time‐dependent density functional theory (TDDFT) make them attractive choices for simulating the spectroscopy of core electrons. An overview of current developments to apply DFT and TDDFT to study the key techniques of X‐ray photoelectron spectroscopy, X‐ray absorption spectroscopy, X‐ray emission spectroscopy, and resonant inelastic X‐ray scattering is presented. Insight into the accuracy that can be achieved, in conjunction with an examination of the limitations and challenges to modeling the spectroscopy of core electrons with DFT is provided. This article is categorized under: Electronic Structure Theory > Ab Initio Electronic Structure Methods Theoretical and Physical Chemistry > Spectroscopy Electronic Structure Theory > Density Functional Theory

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Generalized single excitation configuration interaction: an investigation into the impact of the inclusion of non-orthogonality on the calculation of core-excited states

Abstract: In this paper, we investigate different non-orthogonal generalizations of the configuration interaction with single substitutions (CIS) method and their impact on the calculation of core-excited states.

Cited by 28 publications

References 69 publications

PSIXAS: A Psi4 plugin for efficient simulations of X‐ray absorption spectra based on the transition‐potential and Δ‐Kohn–Sham method

PSIXAS: A Psi4 plugin for efficient simulations of X‐ray absorption spectra based on the transition‐potential and Δ‐Kohn–Sham method

Validity of the static-exchange approximation for inner-shell photoionization of polyatomic molecules

Modeling of the spectroscopy of core electrons with density functional theory

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