Index

Modulated structures dictionary (msCIF) version 3.2.1

_atom_site_displace_special_func.zigzag

Definition:

   

      _atom_site_displace_special_func.zigzag_ items are the
      adjustable parameters of a zigzag function.
      A displacive zigzag function along the internal space is
      defined as follows:

               2*[ax,ay,az]*(x4-c)/w for x4 in [c-(w/2),c+(w/2)]
      [ux,uy,uz] = 
              -2*[ax,ay,az]*(x4-c)/w for x4 in [c+1/2-(w/2),c+1/2+(w/2)]

      where ax,ay and az are the amplitudes (maximum displacements)
      along each crystallographic axis, w is its width, x4 is the
      internal coordinate and c is the centre of the function in
      internal space. ux, uy and uz must be expressed in relative
      units or in angstroms if the modulations are referred to some
      special axes defined by the items belonging to the ATOM_SITES_AXES 
      category, through _atom_site_displace_Fourier.matrix_seq_id.
      The use of this function is restricted to one-dimensional 
      modulated structures. For more details, see (Elcoro et al., 2008; 
      Petricek, Dusek & Palatinus, 2014 and Petricek, Eigner, Dusek 
      & Cejchan, 2016). In the case of rigid groups, items in this 
      category would only include the translational part of the modulation. 
      The rotational part would appear in a separate list of items belonging 
      to the ATOM_SITE_ROT_SPECIAL_FUNC category.

      References: Luis Elcoro, J.M. Perez-Mato, Karen Friese, Vaclav Petricek,
              Tonci Balic-Zunic & Lars Arnskov Olsen (2008)
              Acta Cryst. B64, 684-701. doi:10.1107/S0108768108031492
              Modular crystals as modulated structures: the case of the 
              lillianite homologous series

              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

Type: Real

Values appear in Matrix context.

Dimension: [3]

Evaluation method:

      With  f  as  atom_site_displace_special_func

      atom_site_displace_special_func.zigzag =  [
          
         2 * [f.zigzag_ax, f.zigzag_ay, f.zigzag_az] * 
                     (( zigzag_x4 – f.zigzag_c) / f.zigzag_w )]

Category:
atom_site_displace_special_func