Experimental and four‐component relativistic DFT studies of tungsten carbonyl complexes

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134

189

Section: A Nmr Applicationsmentioning

confidence: 99%

ReSpect: Relativistic spectroscopy DFT program package

Repiský

Komorovský

Kadek

et al. 2020

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134

189

“…The first is that a proper treatment of electron correlation effects is required, and second one has to take into account relativistic effects. The latter problem becomes more pronounced when heavy atoms are present in the molecular systems, as documented by several groups in research articles [3][4][5][6][7][8][9][10][11][12] and reviews. 13,14 The relativistic effects can be interpreted by applying perturbation theory; 15 for example, the effects caused by the interplay between the Fermi-contact (FC) interaction of nucleus K with the spinorbit (SO) interaction generated by the magnetic moment of nucleus L can be analyzed.…”

Section: Introductionmentioning

confidence: 99%

“…This is, for instance, evident from the difference between spin-spin coupling constants calculated using generalized gradient approximation (GGA) and hybrid functionals. 6,10 In our recent work on absolute shielding constants, [31][32][33][34][35] we have shown for various nuclei that both challenges can be overcome and experimental values may be reproduced by combining accurate non-relativistic coupled-cluster results with relativistic corrections obtained from four-component relativistic DFT calculations.…”

Section: Introductionmentioning

confidence: 99%

Indirect NMR spin–spin coupling constants in diatomic alkali halides

Jaszuński

Antušek

Demissie

et al. 2016

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We report the Nuclear Magnetic Resonance (NMR) spin-spin coupling constants for diatomic alkali halides MX, where M = Li, Na, K, Rb, or Cs and X = F, Cl, Br, or I. The coupling constants are determined by supplementing the non-relativistic coupled-cluster singles-and-doubles (CCSD) values with relativistic corrections evaluated at the four-component density-functional theory (DFT) level. These corrections are calculated as the differences between relativistic and non-relativistic values determined using the PBE0 functional with 50% exact-exchange admixture. The total coupling constants obtained in this approach are in much better agreement with experiment than the standard relativistic DFT values with 25% exact-exchange, and are also noticeably better than the relativistic PBE0 results obtained with 50% exact-exchange. Further improvement is achieved by adding rovibrational corrections, estimated using literature data. Published by AIP Publishing. [http://dx

“…8 These methods provide accurate NMR parameters for molecules involving heavy atoms (see for instance Refs. [9][10][11][12][13] ), making them promising and appropriate methods for the study and spectral interpretation of such molecules. However, much work in the area of application of these methods remains to be done, especially for medium-and large-size molecules involving heavy atoms.…”

Section: Introductionmentioning

confidence: 99%

Relativistic effects on the NMR parameters of Si, Ge, Sn, and Pb alkynyl compounds: Scalar versus spin-orbit effects

Demissie

2017

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The NMR chemical shifts and indirect spin-spin coupling constants of 12 molecules containing Si,Ge, Sn, andPb [X(CCMe), MeX(CCMe), and MeXCCH] are presented. The results are obtained from non-relativistic as well as two- and four-component relativistic density functional theory (DFT) calculations. The scalar and spin-orbit relativistic contributions as well as the total relativistic corrections are determined. The main relativistic effect in these molecules is not due to spin-orbit coupling but rather to the scalar relativistic contraction of the s-shells. The correlation between the calculated and experimental indirect spin-spin coupling constants showed that the four-component relativistic density functional theory (DFT) approach using the Perdew's hybrid scheme exchange-correlation functional (PBE0; using the Perdew-Burke-Ernzerhof exchange and correlation functionals) gives results in good agreement with experimental values. The indirect spin-spin coupling constants calculated using the spin-orbit zeroth order regular approximation together with the hybrid PBE0 functional and the specially designed J-coupling (JCPL) basis sets are in good agreement with the results obtained from the four-component relativistic calculations. For the coupling constants involving the heavy atoms, the relativistic corrections are of the same order of magnitude compared to the non-relativistically calculated results. Based on the comparisons of the calculated results with available experimental values, the best results for all the chemical shifts and non-existing indirect spin-spin coupling constants for all the molecules are reported, hoping that these accurate results will be used to benchmark future DFT calculations. The present study also demonstrates that the four-component relativistic DFT method has reached a level of maturity that makes it a convenient and accurate tool to calculate indirect spin-spin coupling constants of "large" molecular systems involving heavy atoms.