Journal of Chemical Physics 133, 084109 (2010)
Dynamical effects in ab initio NMR calculations: Classical force fields fitted to quantum forces
Mark Robinson1 and Peter. D. Haynes2
1Theory of Condensed Matter, Cavendish Laboratory, J. J. Thomson Avenue, Cambridge CB3 0HE, UK
2Departments of Physics and Materials, Imperial College London, Exhibition Road, London SW7 2AZ, UK
NMR chemical shifts for an L-alanine molecular crystal are calculated
using ab initio plane wave density functional theory. Dynamical
effects including anharmonicity may be included by averaging chemical
shifts over an ensemble of structural configurations generated using
molecular dynamics (MD). The time scales required mean that ab
initio MD is prohibitively expensive. Yet the sensitivity of
chemical shifts to structural details requires that the methodologies
for performing MD and calculating NMR shifts be consistent. This work
resolves these previously competing requirements by fitting classical
force fields to reproduce ab initio forces. This methodology is
first validated by reproducing the averaged chemical shifts found
using ab initio molecular dynamics. Study of a supercell of
L-alanine demonstrates that finite size effects can be significant
when accounting for dynamics.
Last updated: 1 September 2010