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Theoretical calculations of heavy atom effects in magnetic resonance spectroscopy
KTH, School of Biotechnology (BIO).
2006 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

This thesis presents quantum chemical calculations, applications of the response function formalism recently implemented within the framework of density functional theory (DFT) by our research group. The purpose of the calculations is to assess the performance of this perturbative approach to determining heavy atom effects on magnetic resonance parameters. Relativistic corrections can be generated by spin-orbit interactions or by scalar relativistic effects due to high velocity electrons in the atomic core region of heavy atoms. In this work, the evaluation of nuclear magnetic resonance (NMR) parameters is considered, the nuclear shielding tensor and the indirect nuclear spin-spin coupling tensor. For series of homologous compounds, it is found that both types of corrections to these parameters are increasing in size upon substitution of a constituent atom by a heavier element, but that their relative importance is system dependent. The obtained results are compatible with the ones provided by electron correlated ab initio methods, and a qualitative agreement with experimentally determined parameters is overall achieved. The methodology presented in this thesis aims to be a practical approach which can be applied in the study of molecular properties of large systems.

This thesis also addresses the calculation of hyperfine coupling constants, and evaluates a novel approach to the treatment of spin-polarization in spin restricted calculations without the spin contamination associated with spin unrestricted calculations.

Place, publisher, year, edition, pages
Stockholm: Bioteknologi , 2006. , v, 28 p.
Keyword [en]
nuclear spin-spin coupling tensor, nuclear shielding tensor, heavy atom effect, hyperfine coupling tensor, restricted-unrestricted approach
National Category
Theoretical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-3971ISBN: 91-7178-351-2 (print)OAI: oai:DiVA.org:kth-3971DiVA: diva2:10226
Presentation
2006-05-30, Sal FB53, AlbaNova, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20101122Available from: 2006-05-17 Created: 2006-05-17 Last updated: 2010-11-22Bibliographically approved
List of papers
1. Density functional theory study of indirect nuclear spin-spin coupling constants with spin-orbit corrections
Open this publication in new window or tab >>Density functional theory study of indirect nuclear spin-spin coupling constants with spin-orbit corrections
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2005 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 123, no 1, 014101-1-014101-10 p.Article in journal (Refereed) Published
Abstract [en]

This work outlines the calculation of indirect nuclear spin-spin coupling constants with spin-orbit corrections using density functional response theory. The nonrelativistic indirect nuclear spin-spin couplings are evaluated using the linear response method, whereas the relativistic spin-orbit corrections are computed using quadratic response theory. The formalism is applied to the homologous systems H2X (X= O, S, Se, Te) and XH4 (X= C, Si, Ge, Sn, Pb) to calculate the indirect nuclear spin-spin coupling constants between the protons. The results confirm that spin-orbit corrections are important for compounds of the H2X series, for which the electronic structure allows for an efficient coupling between the nuclei mediated by the spin-orbit interaction, whereas in the case of the XH4 series the opposite situation is encountered and the spin-orbit corrections are negligible for all compounds of this series. In addition we analyze the performance of the density functional theory in the calculations of nonrelativistic indirect nuclear spin-spin coupling constants.

Keyword
Correlation methods; Electronic structure; Lead compounds; Molecular structure; Nuclear magnetic resonance spectroscopy; Tin compounds; Density functional theory (DFT); Geometrical structures; Molecular systems; Spin-spin coupling constants; Electron energy levels
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-7067 (URN)10.1063/1.1947190 (DOI)000230493600002 ()2-s2.0-22844452433 (Scopus ID)
Note
QC 20100811Available from: 2007-05-11 Created: 2007-05-11 Last updated: 2010-08-11Bibliographically approved
2. Relativistic nuclear shieldings obtained by linear and quadratic density functional response theory
Open this publication in new window or tab >>Relativistic nuclear shieldings obtained by linear and quadratic density functional response theory
(English)Manuscript (Other academic)
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-5750 (URN)
Note
QC 20100624Available from: 2006-05-17 Created: 2006-05-17 Last updated: 2011-02-04Bibliographically approved
3. Time-dependent density functional theory with the generalized restricted-unrestricted approach
Open this publication in new window or tab >>Time-dependent density functional theory with the generalized restricted-unrestricted approach
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2006 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 124, no 17, 174103- p.Article in journal (Refereed) Published
Abstract [en]

This work presents the derivation, implementation, and first applications of the generalized restricted-unrestricted method based on the density functional Kohn-Sham formalism. By using a spin-restricted Kohn-Sham representation for the reference state the well-known spin contamination problem is avoided, while the unrestricted representation of the perturbation response retains a proper description of spin polarization. The formulation is a generalization of our previous implementation of the restricted-unrestricted method [Z. Rinkevicius , J. Chem. Phys. 121, 7614 (2004)], as it accounts for the full unrestricted response instead of describing the spin polarization in terms of triplet operators only. The purpose of this paper is to investigate the role of the generalization employed and demonstrate its numerical performance. For this purpose we focus on isotropic hyperfine coupling constants of a set of organic radicals and transition metal compounds. For both classes of molecules we observe that the effect of neglecting singlet excitation operators in the response part of restricted-unrestricted formalism changes the calculated hyperfine coupling parameters by a few MHz. The obtained results confirm the validity of the approximation used in the simplified restricted-unrestricted approach, i.e. spin polarization can, in most cases, be adequately described by an account of only triplet operators in the response term.

Keyword
Approximation theory; Numerical analysis; Polarization; Quantum theory; Transition metal compounds; Isotropic hyperfine coupling; Singlet excitation operators; Spin polarization; Probability density function
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-7071 (URN)10.1063/1.2191501 (DOI)000237321700005 ()2-s2.0-34547554886 (Scopus ID)
Note
QC 20100811Available from: 2007-05-11 Created: 2007-05-11 Last updated: 2012-03-21Bibliographically approved

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