Xray::Scattering(3pm) User Contributed Perl Documentation Xray::Scattering(3pm)
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.
perl v5.12.4 2011-07-30 Xray::Scattering(3pm)