First-principles calculation of O-17 and Mg-25 NMR shieldings in MgO at finite temperature: Rovibrational effect in solids.

Rossano, S. and Mauri, F. and Pickard, C. J. and Farnan, I. (2005) First-principles calculation of O-17 and Mg-25 NMR shieldings in MgO at finite temperature: Rovibrational effect in solids. Journal of Physical Chemistry B, 109. pp. 7245-7250. DOI 10.1021/jp044251w

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Abstract

The temperature dependence of 17O and 25Mg NMR chemical shifts in solid MgO have been calculated using a first-principles approach. Density functional theory, pseudopotentials, a plane-wave basis set, and periodic boundary conditions were used both to describe the motion of the nuclei and to compute the NMR chemical shifts. The chemical shifts were obtained using the gauge-including projector augmented wave method. In a crystalline solid, the temperature dependence is due to both (i) the variation of the averaged equilibrium structure and (ii) the fluctuation of the atoms around this structure. In MgO, the equilibrium structure at each temperature is uniquely defined by the cubic lattice parameters, which we take from experiment. We evaluate the effect of the fluctuations within a quasiharmonic approximation. In particular, the dynamical matrix, defining the harmonic Hamiltonian, has been computed for each equilibrium volume. This harmonic Hamiltonian was used to generate nuclear configurations that obey quantum statistical mechanics. The chemical shifts were averaged over these nuclear configurations. The results reproduce the previously published experimental NMR data measured on MgO between room temperature and 1000 °C. It is shown that the chemical shift behavior with temperature cannot be explained by thermal expansion alone. Vibrational corrections due to the fluctuations of atoms around their equilibrium position are crucial to reproduce the experimental results.

Item Type: Article
Uncontrolled Keywords: 2005 AREP 2005 P IA48
Subjects: 03 - Mineral Sciences
Divisions: 03 - Mineral Sciences
Journal or Publication Title: Journal of Physical Chemistry B
Volume: 109
Page Range: pp. 7245-7250
Identification Number: 10.1021/jp044251w
Depositing User: Sarah Humbert
Date Deposited: 19 Aug 2010 09:14
Last Modified: 23 Jul 2013 09:59
URI: http://eprints.esc.cam.ac.uk/id/eprint/1804

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