Index

Modulated structures dictionary (msCIF) version 3.2.1

_atom_site_displace_Fourier_param.cos

Definition:

   

      The displacive distortion of a given atom or rigid group (see
      also _atom_site_rot_Fourier_param.cos) 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.cos is the
      cosine coefficient (Ac) corresponding to the Fourier term defined
      _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

Evaluation method:

      With  p  as  atom_site_displace_Fourier_param

       atom_site_displace_Fourier_param.cos =  p.modulus*Cos(TwoPi*p.phase)

Category:
atom_site_displace_Fourier_param