Index

Modulated structures dictionary (msCIF) version 3.2.1

Category ATOM_SITE_DISPLACE_SPECIAL_FUNC

Parent category:
MS_GROUP

Definition:

   

      Data items in the ATOM_SITE_DISPLACE_SPECIAL_FUNC category record
      details about the displacive modulation of an atom site in a
      modulated structure when it is not described by Fourier series.
      Special functions are effective in some cases where the
      modulations are highly anharmonic, since the number of parameters
      is drastically reduced. However, they are in general
      discontinuous or with discontinuous derivatives and therefore
      these functions describe an ideal situation that never occurs
      in a real modulated crystal. Up to now, only a few types of
      special functions have been used and all of them come from the
      JANA2006 suite of programs (Petricek, Dusek & Palatinus, 2014).
      Although this approach is far from
      being general, it has the advantage that the functions are
      tightly defined and therefore the atomic displacements and
      occupations can be calculated easily. In this dictionary,
      only the special functions available in JANA2006 have been
      included. These are:
    (1) Sawtooth functions for the displacive modulation of atoms and 
        rigid groups.
    (2) Zig-Zag functions for the displacive modulation of atoms and
        rigid groups.
    (3) Crenel functions for the occupational modulation of atoms
        and rigid groups. Both of these only apply to
        one-dimensional modulated structures.

      References: Petricek, V., Dusek, M. & Palatinus, L. (2014).
              Z. Kristallogr. 229(5), 345-352.  DOI 10.1515/zkri-2014-1737     
              Crystallographic Computing System JANA2006: General features

              Petricek, V., Eigner, V., Dusek, M. & Cejchan, A. (2016). Z. 
              Kristallogr. 231(5), 301-312. DOI 10.1515/zkri-2015-1913 
              Discontinuous modulation functions and their application for 
              analysis of modulated structures with the computing system JANA2006

Category is of type Loop