NAME¶

Xray::Scattering - X-ray scattering data for the elements

SYNOPSIS¶

  use Xray::Scattering;
  Xray::Scattering->load('CroMann');
  $fnot = Xray::Scattering->get_f($symb, $d);
  Xray::Scattering->load('WaasKirt');
  $fnot = Xray::Scattering->get_f($symb, $d);

DESCRIPTION¶

This module supports access to X-ray scattering data for atoms and ions. It is designed to be a transparent interface to scattering data from a variety of sources. Currently, the only sources of data are the Cromer-Mann tables from the International Tables of Crystallography and the 1995 Waasmaier-Kirfel tables. More resources can be added easily.

METHODS¶

"available"

This method returns a list of data resources available to this module. Currently this returns an array consisting of these strings:

 

  Cromer-Mann  Waasmaier-Kirfel  None
    

 

The first two are functional interfaces to those databases. The third is a fallback subclass which returns default values for all methods.

"get_valence"

This returns the element/valence symbol in the proper form for use with other methods. $elem is a two-letter atomic symbol, and $valence is the valence of the ion. $valence can be an integer, a float, a dot or the string "va".

 

   $symbol = Xray::Scattering->get_valence($elem, $valence)
    

 

Unless the valence is a dot or the string "va", the nearest integer to $valence is used with the element symbol to construct the element/valence symbol. As an example, "$symbol eq "Cu2+"" if "$elem eq "Cu"" and "$valence == 2".

SUBCLASS METHODS¶

All the available subclasses corresponding to the data resources provide their own versions of the following methods:

"get_f"

This function calculates the Thomson scattering for a given symbol and d-spacing. The Thomson scattering depends only on the momentum transfer. The d-spacing of the scattering planes is a closely related quantity and is easily calculated from the crystal structure, see Xtal.pm.

 

  $symb = "Ce3+";
  $fnot = Xray::Scattering->get_f($symb, $d);
    

 

If the symbol cannot be found in the table, "get_f" returns 0. It also returns 0 when $symbol consists of whitespace or is "null" or "nu". If $symbol is a number or the name of an element, then it assumes you want the Thomson scattering for the neutral element. The absolute value of $d_spacing is used by this function.

 

The "None" subclass always returns 0.

 

If you ask for a valence state that is not in the table but for an element whose 0+ state is in the table, this method returns the scattering factor for the 0 valent atom.

"get_coefficients"

This returns the 9 (Cromer-Mann) or 11 (Waasmaier-Kirfel) element list containing the coefficients for the given symbol.

 

   @coefs = Xray::Scattering->get_coefficients($symb)
    

 

See the documents for the subclasses for the order of the coefficients. The None subclass always returns a list of 11 zeros.

 

If you ask for a valence state that is not in the table but for an element whose 0+ state is in the table, this method returns the coefficients for the 0 valent atom.

"has"

This is a test of whether a given symbol is tabulated in the selected data resource table. It returns the symbol itself if found in the table or 0 if it is not in the table.

 

  $symb = "Ce3+";
  $has = Xray::Scattering->has($symb);
    

 

The None subclass returns the symbol itself.

AUTHOR¶

Bruce Ravel, bravel AT bnl DOT gov http://cars9.uchicago.edu/~ravel/software/exafs/

LICENCE AND COPYRIGHT¶

Copyright (c) 2006-2008 Bruce Ravel (bravel AT bnl DOT gov). All rights reserved. This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself. See perlartistic. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.