Index

Modulated structures dictionary (msCIF) version 3.2.1

_atom_site_displace_Fourier_param.modulus

Name:
_atom_site_displace_Fourier_param.modulus

Alias:
_atom_site_displace_Fourier_param_modulus

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 the items belonging to the ATOM_SITES_AXES 
      category, through _atom_site_displace_Fourier.matrix_seq_id.
      Use of _atom_sites_displace_Fourier.axes_description is deprecated 
      and retained only for backward compatibility.

Type: Real

The permitted range is 0.0 → infinity

Enumeration default: 0.0

Evaluation method:

      With  p  as  atom_site_displace_Fourier_param

       atom_site_displace_Fourier_param.modulus =  Sqrt(p.cos**2 + p.sin**2)

Category:
atom_site_displace_Fourier_param