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Electronic g-tensors of solvated molecules using the polarizable continuum model
KTH, Superseded Departments, Biotechnology.
KTH, Superseded Departments, Biotechnology.ORCID iD: 0000-0003-2729-0290
KTH, Superseded Departments, Biotechnology.ORCID iD: 0000-0002-9123-8174
2004 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 121, 5051- p.Article in journal (Refereed) Published
Abstract [en]

We present the implementation of density functional response theory combined with the polarizable continuum model (PCM), enabling first principles calculations of molecular g-tensors of solvated molecules. The calculated g-tensor shifts are compared with experimental g-tensor shifts obtained from electron paramagnetic resonance spectra for a few solvated species. The results indicate qualitative agreement between the calculations and the experimental data for aprotic solvents, whereas PCM fails to reproduce the electronic g-tensor behavior for protic solvents. This failure of PCM for protic solvents can be resolved by including into the model those solvent molecules which are involved in hydrogen bonding with the solute. The results for the protic solvents show that the explicit inclusion of the solvent molecules of the first solvation sphere is not sufficient in order to reproduce the behavior of the electronic g-tensor in protic solvents, and that better agreement with experimental data can be obtained by including the long-range electrostatic effects accounted for by the PCM approach on top of the explicit hydrogen-bonded complexes.

Place, publisher, year, edition, pages
2004. Vol. 121, 5051- p.
Keyword [en]
hyperfine coupling-constants, density-functional calculations, semiquinone radical-anions, nitroxide spin-label, nitric oxide, correlation-energy, orbit operators, linear-response, epr parameters, hartree-fock
National Category
Organic Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-6174DOI: 10.1063/1.1779568ISI: 000223720600005Scopus ID: 2-s2.0-4944231543OAI: oai:DiVA.org:kth-6174DiVA: diva2:10807
Note
QC 20100923 QC 20110916Available from: 2006-09-22 Created: 2006-09-22 Last updated: 2012-03-21Bibliographically approved
In thesis
1. 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
2. Density Functional Theory for EPR and NMR Spin Hamiltonian Parameters
Open this publication in new window or tab >>Density Functional Theory for EPR and NMR Spin Hamiltonian Parameters
2004 (English)Doctoral thesis, comprehensive summary (Other scientific)
Place, publisher, year, edition, pages
Stockholm: KTH, 2004. v, 51 p.
Keyword
DFT, EPR, NMR, response theory
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-3760 (URN)91-7283-748-9 (ISBN)
Public defence
2004-05-27, 00:00
Note
QC 20100622Available from: 2004-05-26 Created: 2004-05-26 Last updated: 2011-09-16Bibliographically approved

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Vahtras, Olav

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