Index

Modulated structures dictionary (msCIF) version 3.2.1

_atom_site_rot_Fourier_param.cos

Definition:

   

      The displacive distortion of a given rigid group is not
      completely described by _atom_site_displace_Fourier.*. The rigid
      rotation of the group around a given axis passing through a fixed
      point (for example, the centre of mass of the group) is usually
      parameterized by Fourier series. Each term of the series
      commonly adopts two different representations: the sine-cosine
      form,
           Rc cos(2\\p k r)+Rs sin(2\\p k r),
      and the modulus-argument form,
           |R| cos(2\\p k r+\\y),
      where k is the wave vector of the term and r is the atomic
      average position. _atom_site_rot_Fourier_param_cos is the cosine
      coefficient (Rc) in degrees corresponding to the Fourier term
      defined by 
      _atom_site_rot_Fourier.atom_site_label,
      _atom_site_rot_Fourier.axis and
      _atom_site_rot_Fourier.wave_vector_seq_id.

Type: Real

Units: degrees

Evaluation method:

      With  p  as  atom_site_rot_Fourier_param

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

Category:
atom_site_rot_Fourier_param