[IUCr Home Page] [CIF Home Page]

Core CIF Dictionary version 2.3




Category: atom_site

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

Must appear in a looped list containing '_atom_site_label'

Enumeration range: 0.0 -> infinity

Related item(s), related function(s):
'_atom_site_B_equiv_geom_mean' alternate '_atom_site_U_iso_or_equiv' conversion

Units: A^2^ ( angstroms squared)


   Isotropic atomic displacement parameter, or equivalent isotropic
   atomic displacement parameter, B(equiv), in angstroms squared,
   calculated from anisotropic temperature factor parameters.

   B(equiv) = (1/3) sum~i~[sum~j~(B^ij^ a*~i~ a*~j~ a~i~ a~j~)]

   a     = the real-space cell lengths
   a*    = the reciprocal-space cell lengths
   B^ij^ = 8 pi^2^ U^ij^

   Ref: Fischer, R. X. & Tillmanns, E. (1988). Acta Cryst. C44,

   The IUCr Commission on Nomenclature recommends against the use
   of B for reporting atomic displacement parameters. U, being
   directly proportional to B, is preferred.

Copyright © 2003 International Union of Crystallography

IUCr Webmaster