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Séminaire Chimie ED459

Solid state NMR, a computational approach

Dr. Robert Laskowski, A*STAR Senior Scientist (Materials Science and Engineering Department, Institute of High Performance Computing, Singapore)

publié le

Le Jeudi 26 octobre 2017 à 14h
ENSCM, Amphithéâtre Mousseron A (campus Balard, 240 av. Émile-Jeanbrau)

Density functional theory [1,2] (DFT) calculations of nuclear magnetic resonance (NMR) shielding in solids present in principle a relatively straightforward way to aid the interpretation of measured spectra. In the case of insulating solids, where only the response of orbital motion contributes to the screening of the external magnetic field, the approach is well-established and has been used for years. [3,4] The situation is much more complicated for metallic systems, where the interaction of the external field with the spin of the electrons leads to repopulation of electronic states around the Fermi level, resulting in a spin current that contributes directly to the screening. The resulting spin density modifies the existing potential and polarizes the lower (core) eigenstates, constituting a source of technical difficulties that may lead to potential issues. For these reasons, there are only very few reported studies of NMR calculations in metals.[5−7] However, these studies also show that carefully approaching such problems can result in reliable computed NMR shielding.

Here I will present a recently developed approach for computing NMR shielding,[8,9] that is applicable for insulating and metallic systems, and implemented in WIEN2k code. Beside that, I will review our recent results computed with the code, present an strategy that can be applied to understand variations of the orbital component of shielding within series of compounds,[10] as well provide some insight into physics of spin contribution constituting Knight shifts.

References

1. W. Kohn, L.J. Sham, Self-consistent equations including exchange and correlation effects. Phys. Rev. 1965, 140, A1133−A1138.
2. P. Hohenberg, W. Kohn, Inhomogeneous electron gas. Phys. Rev. 1964, 136, B864−B871.
3. F. Mauri, B.G. Pfrommer, S.G. Louie, Ab initio theory of NMR chemical shifts in solids and liquids. Phys. Rev. Lett. 1996, 77, 5300−5303.
4. C. J. Pickard, F. Mauri, All-electron magnetic response with pseudopotentials : NMR chemical shifts. Phys. Rev. B : Condens. Matter Mater. Phys. 2001, 63, 245101.
5. R. Laskowski, P. Blaha, NMR shielding in metals using the augmented plane wave method. J. Phys. Chem. C 2015, 119, 19390−19396.
6. R. Laskowski, K. H. Khoo, F. Haarmann, P. Blaha, Computational study of Ga NMR shielding in metallic gallides. J. Phys. Chem. C 2017, 121, 753−760.
7. K. Khoo, R. Laskowki, P. Blaha, Computational study of Al and Sc NMR shielding in metallic ScTT’Al Heusler phases, J. Phys. Chem. C 2017, 121, 12398.
8. R. Laskowski, P. Blaha, Calculations of NMR chemical shifts with APW-based methods. Phys. Rev. B : Condens. Matter Mater. Phys. 2012, 85, 035132.
9. R. Laskowski, P. Blaha, Calculating NMR Chemical shifts using the augmented plane-wave method. Phys. Rev. B : Condens. Matter Mater. Phys. 2014, 89, 014402.
10. R. Laskowski, P. Blaha, Origin of NMR shielding in fluorides. Phys. Rev. B : Condens. Matter Mater. Phys. 2012, 85, 245117.

Biosketch. Robert Laskowski obtained his PhD in 2000 from the University of Technology of Gdansk, Poland. From 2001 to 2013 he was a member of the WIEN2k team. During this time he contributed to develop the WIEN2k code, among others he is an author of non-colinear spin version of WIEN2k, Bethe-Salpeter equation solver, MPI parallelization of the WIEN2k code, and solid state NMR package. From 2013 he has been appointed as senior scientist in the Institute of High Performance Computing, A*STAR, Singapore.

Contact local ICGM : Prof. Gilles Silly (équipe ChV)

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