Paramagnetic NMR chemical shift theory : combined ab initio/densityfunctional theory method 

Author:  Rouf, Syed Awais^{1} 
Organizations: 
^{1}University of Oulu, Faculty of Science, Physics 
Format:  ebook 
Version:  published version 
Access:  open 
Online Access:  PDF Full Text (PDF, 18.2 MB) 
Persistent link:  http://urn.fi/urn:isbn:9789526216850 
Language:  English 
Published: 
2017

Publish Date:  20171003 
Thesis type:  Doctoral Dissertation 
Defence Note:  Academic dissertation to be presented with the assent of the Doctoral Training Committee of Technology and Natural Sciences of the University of Oulu for public discussion in the Auditorium L10, Linnanmaa, on October 13th, 2017, at 12 o’clock noon. 
Tutor: 
Professor Juha Vaara Doctor Jiří Mareš 
Reviewer: 
Professor Radek Marek Doctor Michael Patzschke 
Opponent: 
Professor Tapio Rantala, 
Kustos: 
Professor Juha Vaara 
Description: 
AbstractIn this thesis, the classic KurlandMcGarvey theory for the nuclear magnetic resonance (NMR) chemical shift is presented in a modern framework for paramagnetic systems containing one or more unpaired electrons. Firstprinciples computations are carried out for the NMR shielding tensors in paramagnetic transitionmetal complexes. A combined ab initio/densityfunctional theory (DFT) approach is applied to obtain the necessary electron paramagnetic resonance (EPR) property tensors, i.e., the gtensor, zerofield splitting tensor (D) and hyperfine coupling tensors (A). In DFT, both the generalisedgradient approximation and hybrid DFT are applied to calculate A. The complete active space selfconsistent field theory (CASSCF) and Nelectron valencestate perturbation theory (NEVPT2) are applied to calculate the g and Dtensors. Scalar relativistic effects are included at the secondorder DouglasKrollHess level for the g and Dtensors and, for A, at the fully relativistic fourcomponent matrixDiracKohnSham level. This methodology is applied to study 13C and 1H chemical shifts and shielding anisotropies in a series of Co(II) pyrazolylborate complexes, a Cr(III) quinolylfunctionalised cyclopentadienyl complex, Ni(II) acetylacetonate complexes and various metallocenes. The results obtained from these calculations are generally in a good agreement with the experimental data, in some cases, for Ni(II) complexes, allowing to correct the experimental spectral signal assignment. CASSCF/NEVPT2 computations (especially for the Dtensor) are more accurate than DFT, which is useful for the purpose of obtaining the NMR chemical shifts. The computational results obtained are dependent on the choice of molecular geometry (experimental Xray or computationally optimised), wavefunction used for g and D (CASSCF or NEVPT2), DFT functional for A, and the quality of the basis sets. The locally dense basis method used for the CASSCF/NEVPT2 computations is less expensive and gives equally good results for g and D as fully balanced basis sets. The scalar relativistic influences are usually small for g and D, but are large for A. Due to that, scalar relativistic effects are important for the chemical shift and shielding anisotropy, especially for carbon nuclei. These firstprinciples computations based on combined ab initio/DFT methodology are promising for the treatment of important electron correlation and scalar relativistic effects in the calculation of pNMR chemical shifts and shielding anisotropies. This work provides a straightforward platform for further development of pNMR shielding theory in terms of firstprinciples wavefunctions, as well as for applications in current problems in bio and materials sciences, including lowtemperature experiments. see all

Series: 
Report series in physical sciences 
ISSN:  12394327 
ISSNL:  12394327 
ISBN:  9789526216850 
ISBN Print:  9789526216843 
Issue:  114 
Subjects:  
Copyright information: 
© University of Oulu, 2017. This publication is copyrighted. You may download, display and print it for your own personal use. Commercial use is prohibited. 