Direct, atomic orbital, static exchange calculations of photoabsorption spectra of large molecules and clusters

Ågren, Hans; Carravetta, Vincenzo; Vahtras, Olav; Pettersson, Lars G. M.

doi:10.1016/0009-2614(94)00318-1

Cited by 216 publications

(167 citation statements)

References 16 publications

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“…Assuming this approximation, as we do here, the screening of the occupied levels by the core-excited electron is neglected. The direct SCF program DISCO 24 modified for STEX calculations 25 has been employed in orbital energy and dipole transition moment calculations. The simulated results are presented in Figs.…”

Section: Theoretical Methodsmentioning

confidence: 99%

Resonant and nonresonant x-ray scattering spectra of some poly(phenylenevinylene)s

Guo

Magnuson

Såthe

et al. 1998

The Journal of Chemical Physics

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The electronic structure of some poly͑phenylenevinylene͒s have been investigated by resonant and nonresonant x-ray inelastic scattering spectroscopies. The nonresonant as well as all resonant spectra for each polymer demonstrate benzene-like features, indicating a local character of the x-ray emission in which the phenyl ring acts as a building block. Theoretical simulations of x-ray energies and intensities taking the repeat unit as a model molecule of the polymer agree with the experimental spectra fairly well. The edges of the occupied bands have been identified in the nonresonant spectra of each polymer. By subtracting the emission energy of the highest occupied molecular orbital in the nonresonant spectrum from the core excitation energy in the resonant spectrum an alternative way to determine the optical band gap is obtained. As for free benzene the outer band in the polymer spectra show a depletion of the emission going from the nonresonant to the resonant x-ray emission spectra. It is demonstrated that this transition, which is strictly symmetry forbidden for free benzene, becomes effectively forbidden in the polymer case as a result of strong interference effects, and it is argued that this is the general case for resonant x-ray emission of conjugated polymers as far as the frozen orbital approximation holds.

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Section: Theoretical Methodsmentioning

confidence: 99%

Resonant and nonresonant x-ray scattering spectra of some poly(phenylenevinylene)s

Guo

Magnuson

Såthe

et al. 1998

The Journal of Chemical Physics

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“…(40) and (41)]. For this reason, the double-basis set procedure [137,138] is often used to improve the description of the unoccupied states after SCF convergence (of the occupied orbitals) has been achieved. In this method, the basis set is augmented with extremely diffuse functions on the excited atom, keeping the occupied orbitals constant.…”

Section: Core Electron Excitationsmentioning

confidence: 99%

ERKALE—A flexible program package for X‐ray properties of atoms and molecules

et al. 2012

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ERKALE is a novel software program for computing X-ray properties, such as ground-state electron momentum densities, Compton profiles, and core and valence electron excitation spectra of atoms and molecules. The program operates at Hartree-Fock or density-functional level of theory and supports Gaussian basis sets of arbitrary angular momentum and a wide variety of exchange-correlation functionals. ERKALE includes modern convergence accelerators such as Broyden and ADIIS and it is suitable for general use, as calculations with thousands of basis functions can routinely be performed on desktop computers. Furthermore, ERKALE is written in an object oriented manner, making the code easy to understand and to extend to new properties while being ideal also for teaching purposes.

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“…To this end, a wide range of quantum-chemical methods have been developed for describing excitations from core orbitals (for reviews, see, e.g., Refs [19,22,23]). Widely used are the static-exchange approximation (STEX) [24][25][26], approaches based on tran-sition potential density-functional theory (DFT) [27,28], and time-dependent densityfunctional theory (TD-DFT) [23]. Within TD-DFT, core excitations are accessible by restricting the space of occupied-virtual orbital excitations (restricted-channel approximation) [29,30], by selectively targeting excitations within a specific energy window [31][32][33][34], by using a complex polarization propagator [35,36], or with real-time TD-DFT methods [37].…”

Section: Introductionmentioning

confidence: 99%

Origin-independent calculation of quadrupole intensities in X-ray spectroscopy

Bernadotte

Atkins

Jacob

2012

The Journal of Chemical Physics

147

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For electronic excitations in the ultraviolet and visible range of the electromagnetic spectrum, the intensities are usually calculated within the dipole approximation, which assumes that the oscillating electric field is constant over the length scale of the transition. For the short wavelengths used in hard X-ray spectroscopy, the dipole approximation may not be adequate. In particular, for metal K-edge X-ray absorption spectroscopy (XAS), it becomes necessary to include higher-order contributions. In quantum-chemical approaches to X-ray spectroscopy, these socalled quadrupole intensities have so far been calculated by including contributions depending on the square of the electric-quadrupole and magnetic-dipole transition moments. However, the resulting quadrupole intensities depend on the choice of the origin of the coordinate system. Here, we show that for obtaining an originindependent theory, one has to include all contributions that are of the same order in the wave vector consistently. This leads to two additional contributions depending on products of the electric-dipole andelectric-octupole and of the electric-dipole and magnetic-quadrupole transition moments, respectively. We have implemented such an origin-independent calculation of quadrupole intensities in XAS within timedependent density-functional theory, and demonstrate its usefulness for the calculation of metal and ligand K-edge XAS spectra of transition metal complexes.2

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Direct, atomic orbital, static exchange calculations of photoabsorption spectra of large molecules and clusters

Cited by 216 publications

References 16 publications

Resonant and nonresonant x-ray scattering spectra of some poly(phenylenevinylene)s

Resonant and nonresonant x-ray scattering spectra of some poly(phenylenevinylene)s

ERKALE—A flexible program package for X‐ray properties of atoms and molecules

Origin-independent calculation of quadrupole intensities in X-ray spectroscopy

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