Modulated Structures CIF Dictionary version 1.0

_atom_site_displace_Fourier_param_modulus

Name

Category: atom_site_displace_Fourier_param

Data type: numb (with optional s.u. in parentheses)

Must appear in a looped list containing '_atom_site_displace_Fourier_param_id'

Enumeration range: 0.0 -> infinity
Enumeration default: 0.0

Definition

    	
   The displacive distortion of a given atom or rigid group (see
   also _atom_site_rot_Fourier_param_modulus) is usually 
   parameterized by Fourier series. Each term of the series commonly
   adopts two different representations: the sine-cosine form,
            Ac cos(2\p k r)+As sin(2\p k r);
   and the modulus-argument form,
            |A| cos(2\p k r+\f);
   where k is the wave vector of the term and r is the atomic
   average position. _atom_site_displace_Fourier_param_modulus is 
   the modulus (|A|) of the complex amplitude corresponding to the
   Fourier term defined by
   _atom_site_displace_Fourier_atom_site_label,
   _atom_site_displace_Fourier_axis, and
   _atom_site_displace_Fourier_wave_vector_seq_id. Atomic or rigid
   group displacements must be expressed as fractions of the unit
   cell or in angstroms if the modulations are referred to some
   special axes defined by
   _atom_sites_displace_Fourier_axes_description.