NAME

       Xray::Scattering::WassKirf - Perl interface to the Waaskirf-Kirfel tables

SYNOPSIS

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

DESCRIPTION

       This module provides a functional interface to the Waasmaier-Kirfel tables of coefficients
       for calculating the Thomson (kinematical) scattering factors of the elements and common
       valence states.  The coefficients are stored externally in the waaskirf.db database file.
       The coefficients are for an Aikman expansion, which is of this form:

                 5
           f0 = sum [ ai*exp(-bi*s^2) ] + c
                i=1

       Thus there are 11 coefficients for each of the 211 tabulated element/valence symbols.

       "s" is "sin(theta)/lambda".  "(lambda*s)/2pi" is the momentum transfer.  "s" is simply
       related to the crystal d-spacing by "s=1/2d".

       The reference for these tables is "New Analytical Scattering Factor Functions for Free
       Atoms and Ions for Free Atoms and Ions", D. Waasmaier & A. Kirfel, Acta Cryst. (1995) A51,
       pp. 416-413.  [doi:10.1107/S0108767394013292] These data, computed for neutral atoms and
       ions, are valid for the full range of sin(theta)/lambda from 0.0 to 6.0 A-1.

       The actual data used in the W-K Aikman expansion can be found in a few places on the web.
       Here is where I obtained the file used with this module:
       http://ftp.esrf.fr/pub/scisoft/xop/DabaxFiles/f0_WaasKirf.dat

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.

           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 11 element list containing the coefficients for the given symbol.

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

           This returns a1,b1,a2,b2,a3,b3,a4,b4,c.

           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 Waasmaier-Kirfel table.
           It returns the symbol itself if found in the table or 0 if it is not in the table.

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

ELEMENTS AND VALENCE STATES

       The following is a list of symbols for the tabulated elements and valence states.  The
       final two are ways of refering to an empty site (i.e. a null or blank atom).

         H     H1-   He    Li    Li1+    Be    Be2+   B     C
         Cval  N     O     O1-   O2-     F     F1-    Ne    Na
         Na1+  Mg    Mg2+  Al    Al3+    Si    Siva   Si4+  P
         S     Cl    Cl1-  Ar    K       K1+   Ca     Ca2+  Sc
         Sc3+  Ti    Ti2+  Ti3+  Ti4+    V     V2+    V3+   V5+
         Cr    Cr2+  Cr3+  Mn    Mn2+    Mn3+  Mn4+   Fe    Fe2+
         Fe3+  Co    Co2+  Co3+  Ni      Ni2+  Ni3+   Cu    Cu1+
         Cu2+  Zn    Zn2+  Ga    Ga3+    Ge    Ge4+   As    Se
         Br    Br1-  Kr    Rb    Rb1+    Sr    Sr2+   Y     Zr
         Zr4+  Nb    Nb3+  Nb5+  Mo      Mo3+  Mo5+   Mo6+  Tc
         Ru    Ru3+  Ru4+  Rh    Rh3+    Rh4+  Pd     Pd2+  Pd4+
         Ag    Ag1+  Ag2+  Cd    Cd2+    In    In3+   Sn    Sn2+
         Sn4+  Sb    Sb3+  Sb5+  Te      I     I1-    Xe    Cs
         Cs1+  Ba    Ba2+  La    La3+    Ce    Ce3+   Ce4+  Pr
         Pr3+  Pr4+  Nd    Nd3+  Pm      Pm3+  Sm     Sm3+  Eu
         Eu2+  Eu3+  Gd    Gd3+  Tb      Tb3+  Dy     Dy3+  Ho
         Ho3+  Er    Er3+  Tm    Tm3+    Yb    Yb2+   Yb3+  Lu
         Lu3+  Hf    Hf4+  Ta    Ta5+    W     W6+    Re    Os
         Os4+  Ir    Ir3+  Ir4+  Pt      Pt2+  Pt4+   Au    Au1+
         Au3+  Hg    Hg1+  Hg2+  Tl      Tl1+  Tl3+   Pb    Pb2+
         Pb4+  Bi    Bi3+  Bi5+  Po      At    Rn     Fr    Ra
         Ra2+  Ac    Ac3+  Th    Th4+    Pa    U      U3+   U4+
         U6+   Np    Np3+  Np4+  Np6+    Pu    Pu3+   Pu4+  Pu6+
         Am    Cm    Bk    Cf    ' '     Nu

AUTHOR

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