The superstructure determination of displacive distortions via symmetry-mode analysis

Acta Crystallographica. Section A, Foundations of Crystallography
Sean KermanJohn S O Evans

Abstract

For any crystal structure that can be viewed as a low-symmetry distortion of some higher-symmetry parent structure, one can represent the details of the distorted structure in terms of symmetry-adapted distortion modes of the parent structure rather than the traditional list of atomic xyz coordinates. Because most symmetry modes tend to be inactive, and only a relatively small number of mode amplitudes are dominant in producing the observed distortion, symmetry-mode analysis can greatly simplify the determination of a displacively distorted structure from powder diffraction data. This is an important capability when peak splittings are small, superlattice intensities are weak or systematic absences fail to distinguish between candidate symmetries. Here, the symmetry-mode basis is treated as a binary (on/off) parameter set that spans the space of all possible P1 symmetry distortions within the experimentally determined supercell. Using the average R(wp) over repeated local minimizations from random starting points as a cost function for a given mode set, global search strategies are employed to identify the active modes of the distortion. This procedure automatically yields the amplitudes of the active modes and the associated a...Continue Reading

References

Jun 1, 1985·Physical Review. B, Condensed Matter·H T Stokes, D M Hatch
Aug 20, 2010·Acta Crystallographica. Section A, Foundations of Crystallography·J M Perez-MatoM I Aroyo
Jun 10, 2009·Journal of Physics. Condensed Matter : an Institute of Physics Journal·Jing ZhaoTadeusz Lukasiewicz

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Citations

Oct 19, 2012·Inorganic Chemistry·Joke HadermannEvgeny V Antipov
Oct 27, 2015·Journal of Applied Crystallography·James R Neilson, Tyrel M McQueen
Jun 4, 2016·Physical Review Letters·M S SennA L Goodwin
Jun 3, 2017·Acta Crystallographica Section B, Structural Science, Crystal Engineering and Materials·Chun Hai WangKevin Steven Knight
Jan 4, 2017·Acta Crystallographica. Section A, Foundations and Advances·Mark S Senn
Aug 17, 2018·Journal of Chemical Information and Modeling·Nicholas WagnerJames M Rondinelli

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