Relativistic corrections for single- and double-core excitation at the K- and L-edges from Li to Kr

Takahashi, Osamu

doi:10.1016/j.comptc.2017.01.007

Cited by 15 publications

(19 citation statements)

References 61 publications

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“…We do however note that the experimental values are not particularly precise, with the vibrational frequency being estimated from an experiment with a photon resolution of approx 50 meV (i.e., 403 cm −1 ) and the bond length being calculated via a fit to a Morse potential, 120 which does not appear SiH 4 , PH 3 , H 2 S, and HCl employ aug-cc-pCVTZ, while the mixed basis strategy described above was used for the remaining species (aug-cc-pCVTZ as the large local basis and aug-cc-pVDZ for other atoms). Scalar relatvistic corrections for these atoms are <0.1 eV 86 and were thus neglected. The protocol for incorporating spin−orbit coupling is described in Computational Methods.…”

Section: T H I S C O N T E N T Imentioning

confidence: 99%

Highly Accurate Prediction of Core Spectra of Molecules at Density Functional Theory Cost: Attaining Sub-electronvolt Error from a Restricted Open-Shell Kohn–Sham Approach

Hait

Head‐Gordon

2020

J. Phys. Chem. Lett.

130

182

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We present the use of the recently developed Square Gradient Minimization (SGM) algorithm for excited state orbital optimization, to obtain spin-pure Restricted Open-Shell Kohn-Sham (ROKS) energies for core excited states of molecules. The SGM algorithm is robust against variational collapse, and offers a reliable route to converging orbitals for target excited states at only 2-3 times the cost of ground state orbital optimization (per iteration). ROKS/SGM with the modern SCAN/ωB97X-V functionals is found to predict the K edge of C,N,O and F to a root mean squared error of ∼0.3 eV. ROKS/SGM is equally effective at predicting L edge spectra of third period elements, provided a perturbative spin-orbit correction is employed. This high accuracy can be contrasted with traditional TDDFT, which typically has greater than arXiv:1912.05249v2 [physics.chem-ph] 9 Jan 2020 10 eV error and requires translation of computed spectra to align with experiment.ROKS is computationally affordable (having the same scaling as ground state DFT, and a slightly larger prefactor) and can be applied to geometry optimizations/ab-initio molecular dynamics of core excited states, as well as condensed phase simulations. ROKS can also model doubly excited/ionized states with one broken electron pair, which are beyond the ability of linear response based methods.Spectroscopy of core electrons is an useful tool for characterizing local electronic structure in molecules and extended materials, and has consequently seen wide use for studying both static properties 1-3 and dynamics 4-6 of chemical systems. Theoretical modeling of core excited states is however a challenging task, as traditional quantum chemistry methods are typically geared towards understanding behavior of valence electrons. Indeed, it is common practice to 'shift' computed X-ray absorption spectra (XAS) by several eV to align with experiment. 7-12 Such uncontrolled translation of spectra for empirical mitigation of systematic error is quite unappealing, and creates considerable scope for incorrect assignments.Linear response (LR) methods like time dependent density functional theory (TDDFT) [13][14][15] and equation of motion coupled cluster (EOM-CC) 16,17 are widely used to model excitations.LR methods do not require prior knowledge about the nature of targeted states, as they permit simultaneous calculation of multiple states on an even footing. However, widely used LR methods only contain a limited description of orbital relaxation, leading to poor performance for cases where such effects are essential (such as double excitations, 18-20 as well as charge-transfer 15,21 and Rydberg states 18,22 in the case of TDDFT). Core excitations in particular are accompanied by substantial relaxation of the resulting core-hole (as well as relaxation of the valence density in response), leading to rather large errors with standard LR protocols. For instance, TDDFT spectra often need to be blue-shifted by > 10 eV to correspond to experiment 7-10 (unless short-range corrected functionals spec...

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Section: T H I S C O N T E N T Imentioning

confidence: 99%

Highly Accurate Prediction of Core Spectra of Molecules at Density Functional Theory Cost: Attaining Sub-electronvolt Error from a Restricted Open-Shell Kohn–Sham Approach

Hait

Head‐Gordon

2020

J. Phys. Chem. Lett.

130

182

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“…An atomic relativistic correction calculated via the Douglas-Kroll-Hell method, found to be nearly independent of basis-set and molecule for the main group elements, is added to all calculations (0.012, 0.09, 0.18, 0.34, 0.57, and 0.91 eV for Be, C, N, O, F, and Ne.) 64 For two of the three schemes of ∆CC we employ, the calculated singlet excited states are spin contaminated; the AP method is used to estimate the spin-pure excitation energies.…”

Section: Computational Detailsmentioning

confidence: 99%

Core excitations: how far can we push correlated single-reference formalism for Delta-based methods?

Arias-Martinez,

Cunha,

Oosterbaan

et al. 2022

Preprint

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We investigate the use of orbital-optimized references in conjunction with singlereference coupled-cluster theory with single and double substitutions (CCSD) for the study of core excitations and ionizations of 18 small organic molecules, without any use of response theory or equation-of-motion formalisms. Three schemes are employed to successfully address the convergence difficulties associated with the coupled-cluster equations, and the spin contamination resulting from the use of a spin symmetry-broken reference, in the case of excitations. In order to gauge the inherent potential of the methods studied, an effort is made to provide reasonable basis set limit estimates for the transition energies. Overall, we find that the two best-performing schemes studied here for ∆CCSD are capable of predicting excitation and ionization energies with errors comparable to experimental accuracies. The proposed ∆CCSD schemes seem to fare

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“…Transition energies (eV) for core excited states in methane, ammonia, and water. Experimental transition energies have been adjusted to remove relativistic effects 67 and in one case a hot vibrational quanta. 68 Theoretical results (for both ground-to-excited and excited-to-excited transition energies) are reported as errors relative to the adjusted experimental numbers.…”

Section: A Transition Energiesmentioning

confidence: 99%

A variational Monte Carlo approach for core excitations

Garner

Neuscamman

2020

The Journal of Chemical Physics

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We present a systematically-improvable approach to core excitations in variational Monte Carlo. Building on recent work in excited-state-specific Monte Carlo, we show how a straightforward protocol, starting from a quantum chemistry guess, is able to capture core state's strong orbital relaxations, maintain accuracy in the near-nuclear region during these relaxations, and explicitly balance accuracy between ground and core excited states. In water, ammonia, and methane, which serve as prototypical representatives for oxygen, nitrogen, and carbon core states, respectively, this approach delivers accuracies on par with the best available theoretical methods even when using relatively small wave function expansions.

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Relativistic corrections for single- and double-core excitation at the K- and L-edges from Li to Kr

Cited by 15 publications

References 61 publications

Highly Accurate Prediction of Core Spectra of Molecules at Density Functional Theory Cost: Attaining Sub-electronvolt Error from a Restricted Open-Shell Kohn–Sham Approach

Highly Accurate Prediction of Core Spectra of Molecules at Density Functional Theory Cost: Attaining Sub-electronvolt Error from a Restricted Open-Shell Kohn–Sham Approach

Core excitations: how far can we push correlated single-reference formalism for Delta-based methods?

A variational Monte Carlo approach for core excitations

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