NAME

       Xray::Scattering::CromerMann - Perl interface to Thomspon scattering factors

SYNOPSIS

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

DESCRIPTION

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

                 4
           f0 = sum [ ai*exp(-bi*s^2) ] + c
                i=1

       Thus there are 9 coefficients for each of the 213 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 data for these tables can be found in Volume C of the International Tables of
       Crystallography, ed. A.J.C. Wilson, published by IUCr and Kluwer Academic Publishers
       (1992).  The table starts on page 500 and a discussion can be found on page 487.

       These tables are known to be inaccurate, particularly at high angles.  This module is a
       toy.  It is suitable for a student or for the sort of quick-n-dirty crystallographic
       hackery that the author indulges in.

CLASS 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 9 element list containing the coefficients for the given symbol.

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

           Returns the array 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 Cromer-Mann 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      H.     H1-    He     Li     Li1+   Be
             Be2+   B      C      C.     N      O      O1-
             F      F1-    Ne     Na     Na1+   Mg     Mg2+
             Al     Al3+   Si     Si.    Si4+   S      P
             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      Y3+    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     O2-.   ' '    Nu

AUTHOR

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