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Time-dependent density functional theory with the generalized restricted-unrestricted approach
KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).ORCID iD: 0000-0003-2729-0290
KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).ORCID iD: 0000-0002-9123-8174
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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.

Place, publisher, year, edition, pages
2006. Vol. 124, no 17, 174103- p.
Keyword [en]
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: urn:nbn:se:kth:diva-7071DOI: 10.1063/1.2191501ISI: 000237321700005Scopus ID: 2-s2.0-34547554886OAI: oai:DiVA.org:kth-7071DiVA: diva2:11973
Note
QC 20100811Available from: 2007-05-11 Created: 2007-05-11 Last updated: 2012-03-21Bibliographically approved
In thesis
1. Density Functional Response Theory with Applications to Electron and Nuclear Magnetic Resonance
Open this publication in new window or tab >>Density Functional Response Theory with Applications to Electron and Nuclear Magnetic Resonance
2007 (English)Doctoral 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 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 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: KTH, 2007. v, 51 p.
Keyword
biochemistry, molecular physics, computer science
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-4367 (URN)978-91-7178-675-3 (ISBN)
Public defence
2007-05-25, FA32, AlbaNova, Roslagstullsbacken, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100811Available from: 2007-05-11 Created: 2007-05-11 Last updated: 2010-08-11Bibliographically approved
2. Theoretical calculations of heavy atom effects in magnetic resonance spectroscopy
Open this publication in new window or tab >>Theoretical calculations of heavy atom effects in magnetic resonance spectroscopy
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
nuclear spin-spin coupling tensor, nuclear shielding tensor, heavy atom effect, hyperfine coupling tensor, restricted-unrestricted approach
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-3971 (URN)91-7178-351-2 (ISBN)
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
3. Density functional studies of EPR and NMR parameters of paramagnetic systems
Open this publication in new window or tab >>Density functional studies of EPR and NMR parameters of paramagnetic systems
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Experimental methods based on the magnetic resonance phenomenon belong to the most widely used experimental techniques for investigations of molecular and electronic structure. The difficulty with such experiments, usually a proper interpretation of data obtained from high-resolution spectra, opens new challenges for pure theoretical methods. One of these methods is density functional theory (DFT), that now has an advanced position among a whole variety of computational techniques. This thesis constitutes an effort in this respect, as it presents theory and discusses calculations of electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) parameters of paramagnetic molecules. It is known that the experimental determination of the magnetic resonance parameters of such molecules, especially in the case of NMR, is quite complicated and requires special techniques of spectral detection. On the other hand, paramagnetics play an important role in many areas, such as molecular magnets, active centers in biological systems, and defects in inorganic conductive materials. Therefore, they have spurred great interest among experimentalists, motivating us to facilitate the interpretation of spectral data through theoretical calculations. This thesis describes new methodologies for the determination of magnetic properties of paramagnetic molecules in the framework of DFT, which have been developed in our laboratory, and their applications in calculations of a wide range of molecular systems.

The first two papers of this thesis deal with the theoretical determination of NMRparameters, such as nuclear shielding tensors and chemical shifts, in paramagnetic nitroxides that form core units in molecular magnets. The developed methodology is aimed to realize a high calculational accuracy for these systems. The effects of hydrogen bonding are also described in that context. Our theory for the evaluation of nuclear shielding tensors in paramagnetic molecules is consistent up to second order in the fine structure constant and considers orbital, fully anisotropic dipolar, and isotropic contact contributions to the shielding tensor.

The next projects concern electron paramagnetic resonance. The well-known EPR parameters, such as the g-tensors and the hyperfine coupling constants are explored. Calculations of electronic g-tensors were carried out in the framework of a spin-restricted open-shell Kohn-Sham method combined with the linear response theory recently developed in our laboratory and allowing us to avoid by definition the spin-contamination problem. The inclusion of solvent effects, described by the polarizable continuum model, extends the possibility to treat molecular systems often investigated in solution. For calculations of the hyperfine coupling constants a so-called restricted-unrestricted approach to account for the spin polarization effect has been developed in the context of DFT. To examine the validity of the approximations implicit in this scheme, the neglect ii of singlet operators, a generalized RU methodology was implemented, which includes a fully unrestricted treatment with both singlet and triplet operators. The small magnitude of the changes in hyperfine coupling constants confirms the validity of the original scheme.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. 50 p.
Keyword
spin-restricted DFT, restricted-unrestricted approach, EPR spin Hamiltonian parameters, NMR spin Hamiltonian parameters
National Category
Organic Chemistry
Identifiers
urn:nbn:se:kth:diva-4116 (URN)91-7178-450-0 (ISBN)
Public defence
2006-10-06, FD5, AlbaNova, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100923Available from: 2006-09-22 Created: 2006-09-22 Last updated: 2012-03-21Bibliographically approved

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Vahtras, OlavÅgren, Hans

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