Software Section - VALENCE and VALIST

Inorganic structures can be checked and analysed using bond valences which are the electrostatic fluxes linking cations to anions (Preiser, Loesel, Brown, Kunz and Skowron, Acta Cryst. B in press). Gauss' law states that the sum of the bond valences around any atom is equal to the formal ionic charge of that ion, and experimental studies have shown that it correlates closely with bond length. Thus bond lengths can be used to determine bond valences and comparing the bond valence sum with the formal charge on an atom is a useful way of confirming the correctness of a crystal structure determination. Individual bond valences give an idea of the strength of individual bonds and hence their importance in crystal chemistry, and the valence sums can be used to determine the oxidation state of an atom or the relative proportions of different atoms on a particular site.

Two programs, VALENCE and VALIST, are available to assist in this analysis. VALENCE is a DOS program that calculates the bond valence when the bond length is entered from the keyboard (Brown, (1996) J. Appl. Cryst. 29, 479-480). It will also calculate the bond length if the bond valence is entered. VALIST is Windows (9x and NT) based and automatically calculates the bond valences for each of the bonds listed in an input file which may be in the format of CIF, GSAS or Fullprof output, or the bond length files produced by ICSD for WWW. VALIST can also be used to determine the relative occupation numbers of two atoms occupying the same site.

Both programs contain the parameters needed for this calculation but these parameters can be changed from within the program if necessary. VALENCE provides the means for determining these parameters from experimental observation. The parameters used by VALIST reside on an external file which can be edited by the user.

Although bond valences are based on the ionic model, they can be used for salts, minerals and ceramic materials and are particularly useful in analysing lattice induced bond strains such as those found in perovskites (Brown (1992) Acta Cryst. B48, 553- 572).

VALENCE is available from the CCP14 web site:

a href="http://www.ccp14.ac.uk/ccp/web-mirrors/valence"> http://www.ccp14.ac.uk/ccp/web-mirrors/valence

or from David Brown email: [email protected].

VALIST is available from the ILL web site:


ftp://ftp.ill.fr/pub/dif/valist

or from the author, Andrew Wills email: [email protected].

David Brown
Brockhouse Institute for Materials Research,
McMaster University, Hamilton, Ontario, Canada

Page last updated 29 May 1999

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