Intermediate Hamiltonian Fock Space Multireference Coupled Cluster Approach to Core Excitation Spectra

Dutta, Achintya Kumar; Gupta, Jitendra; Vaval, Nayana; Pal, Sourav

doi:10.1021/ct500285e

Cited by 27 publications

(39 citation statements)

References 85 publications

(145 reference statements)

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“…In contrast to CI, the extension of the CC idea to the MR case is nontrivial due to the problem with definition of a proper vacuum state leading to a number of technical complications, for review see Reference . However, various flavors of MR CC have been applied to core spectra of small main group molecules recently …”

Section: Theoretical Methodsmentioning

confidence: 99%

Theoretical X‐ray spectroscopy of transition metal compounds

Bokarev

Kühn

2019

WIREs Comput Mol Sci

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X-ray spectroscopy is one of the most powerful tools to access structure and properties of matter in different states of aggregation as it allows to trace atomic and molecular energy levels in course of various physical and chemical processes. Xray spectroscopic techniques probe the local electronic structure of a particular atom in its environment, in contrast to ultraviolet/visible (UV/Vis) spectroscopy, where transitions generally occur between delocalized molecular orbitals. Complementary information is provided by using a combination of different absorption, emission, scattering as well as photo-and autoionization X-ray methods. However, interpretation of the complex experimental spectra and verification of experimental hypotheses is a nontrivial task and powerful first principles theoretical approaches that allow for a systematic investigation of a broad class of systems are needed. Focusing on transition metal compounds, L-edge spectra are of particular relevance as they probe the frontier d-orbitals involved in metal-ligand bonding. Here, neardegeneracy effects in combination with spin-orbit coupling lead to a complicated multiplet energy level structure, which poses a serious challenge to quantum chemical methods. Multiconfigurational self-consistent field (MCSCF) theory has been shown to be capable of providing a rather detailed understanding of experimental X-ray spectroscopy. However, it cannot be considered as a "blackbox" tool and its application requires not only a command of formal theoretical aspects, but also a broad knowledge of already existing applications. Both aspects are covered in this overview.

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Section: Theoretical Methodsmentioning

confidence: 99%

Theoretical X‐ray spectroscopy of transition metal compounds

Bokarev

Kühn

2019

WIREs Comput Mol Sci

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“…Table 2 shows the CVS-ODC-12 results for 36 core-level transitions of 10 molecules. For comparison, we also show best available theoretical results obtained from various formulations of coupled cluster theory, 34,39,41,43,44 as well as excitation energies measured in the experiment. [88][89][90][91][92][93][94][95][96][97][98][99][100][101][102] For all electronic transitions, the CVS-ODC-12 method correctly reproduces the order of peaks observed in the experimental spectra with transitions shifted to higher energies.…”

Section: Excitations Energiesmentioning

confidence: 99%

“…Many of the popular excited-state methods have been adopted for simulations of X-ray absorption spectra, including linearresponse, [9][10][11][12][13][14] real-time, [15][16][17] and orthogonalityconstrained 18,19 density functional theory, configuration interaction, [20][21][22][23][24][25] algebraic diagram-matic construction (ADC), 5,[26][27][28][29][30] as well as linear-response (LR-) and equation-of-motion (EOM-) coupled cluster (CC) theories. [31][32][33][34][35][36][37][38][39][40][41][42][43][44] Among these approaches, CC methods have been shown to yield particularly accurate results for core excitation energies and intensities of small molecules.…”

Section: Introductionmentioning

confidence: 99%

Simulating X-ray Absorption Spectra with Linear-Response Density Cumulant Theory

2019

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We present a new approach for simulating Xray absorption spectra based on linear-response density cumulant theory (LR-DCT) [Copan, A. V.; Sokolov, A. Yu. J. Chem. Theory Comput., 2018, 14, 4097-4108]. Our new method combines the LR-ODC-12 formulation of LR-DCT with core-valence separation approximation (CVS) that allows to efficiently access high-energy core-excited states. We describe our computer implementation of the CVS-approximated LR-ODC-12 method (CVS-ODC-12) and benchmark its performance by comparing simulated X-ray absorption spectra to those obtained from experiment for several small molecules. Our results demonstrate that the CVS-ODC-12 method shows a good agreement with experiment for relative spacings between transitions and their intensities, but the excitation energies are systematically overestimated. When comparing to results from excited-state coupled cluster methods with single and double excitations, the CVS-ODC-12 method shows a similar performance for intensities and peak separations, while coupled cluster spectra are less shifted, relative to experiment. An important advantage of CVS-ODC-12 is that its excitation energies are computed by diagonalizing a Hermitian matrix, which enables efficient computation of transition intensities. arXiv:1812.08827v2 [physics.chem-ph]

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“…Among the different variants of EOM methods available, the equation of motion coupled cluster (EOM‐CC) method provides the most systematic way for balanced inclusion of dynamic and nondynamic correlation effects. The EOM‐CC approach for the ionization problem (EOMIP‐CC) is generally used in singles and doubles truncation (EOMIP‐CCSD) and provides an easy way to (0,1) sector of Fock space, without venturing into the conceptual difficulties of the corresponding multireference coupled cluster (FSMRCC) method . The EOMIP‐CCSD method scales as O(N 6 ) power of the basis set and has similar storage requirement as that of the single‐reference coupled cluster method, which prohibits its use beyond medium‐sized molecules in any reasonable basis set.…”

Section: Introductionmentioning

confidence: 99%

“…The EOM-CC approach for the ionization problem [14] (EOMIP-CC) is generally used in singles and doubles truncation (EOMIP-CCSD) and provides an easy way to (0,1) sector of Fock space, [15] without venturing into the conceptual difficulties of the corresponding multireference coupled cluster (FSMRCC) method. [16][17][18] The EOMIP-CCSD method scales as O(N 6 ) power of the basis set and has similar storage requirement as that of the single-reference coupled cluster method, which prohibits its use beyond medium-sized molecules in any reasonable basis set.The coupled cluster method shares an intriguing relationship with many-body perturbation theory. [19] So, the most obvious way of deriving an approximation to the coupled cluster method is based on perturbation orders.…”

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confidence: 99%

Lower scaling approximation to EOM‐CCSD: A critical assessment of the ionization problem

Dutta

Vaval

Pal

2018

Int J of Quantum Chemistry

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In this article, we investigate the performance of different approximate variants of the EOM‐CCSD method for calculation of ionization potential (IP), as compared to EOM‐CCSDT reference values. None of the lower scaling approximations to the EOM‐CCSD method give a consistent performance for valence, inner valence, and core ionization, favoring one, or the other depending on the nature of the approximation used. The parent EOMIP‐CCSD method gives superior performance for valence IP but can show large errors for inner valence and core ionization. The problem is particularly severe for core‐ionization, where even the EOMIP‐CCSDT method cannot provide quantitative accuracy.

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Intermediate Hamiltonian Fock Space Multireference Coupled Cluster Approach to Core Excitation Spectra

Cited by 27 publications

References 85 publications

Theoretical X‐ray spectroscopy of transition metal compounds

Theoretical X‐ray spectroscopy of transition metal compounds

Simulating X-ray Absorption Spectra with Linear-Response Density Cumulant Theory

Lower scaling approximation to EOM‐CCSD: A critical assessment of the ionization problem

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