RELATION, Version 1.0, June 2000

Harold T. Stokes
Department of Physics and Astronomy, Brigham Young University, Provo, Utah
e-mail: stokesh@byu.edu

This program may be distributed without restriction, but if it is used
in research that results in publications, the use of this program
should be acknowledged.

This program determines if two crystals have a group-subgroup relation.

See relation_sample*.in and relation_sample*.out for sample input and
output files to this program.

This program is accompanied by two binary data files, data_space.bin
and data_wyckoff.bin, which the program reads when it starts.

The linux version of this program requires an environment variable
ISODATA which contains the full path to the directory containing the
data files. For example, if the full path is
/usr/local/common/isobyu/, then the command in c shell would be:

setenv ISODATA /usr/local/common/isobyu/

The standard input should contain the following information:

(1) Title line.  This line is copied to the output, but is otherwise
ignored by the program.  There must be at least one nonblank character
on this line.

(2) Space group of the first crystal.  Enter the space group number
(1-230).  

(4) Lattice parameters of the first crystal structure:
a,b,c,alpha,beta,gamma.  The lengths a,b,c may be given in any units.
The angles alpha,beta,gamma must be given in degrees.  For
rhombohedral space groups, the lattice parameters must be given for
the hexagonal axes.

(5) The number of Wyckoff positions in the first crystal.

(6) Information about each Wyckoff position in the first crystal: The
atomic symbol (eg., Ba, Si, H), the Wyckoff position (eg., a, b, c),
the parameters x,y,z for the Wyckoff position, as listed in the
International Tables of Crystallography.  Each Wyckoff position must
be entered on a separate line.  The same atomic symbol must be used
for the same kind of atoms (eg., do not use Cu1 and Cu2 for Cu atoms
at two different Wyckoff positions unless you do not want the program
to consider them interchangeable).

If you do not know the Wyckoff position, enter * for the position and
then give the x,y,z coordinates of one of the atoms at that position.
If you use this option, then the space group setting makes a
difference.  (Wyckoff positions and parameters are independent of
setting.)  This program uses the following settings: for monoclinic,
unique axis b and cell choice 1; for rhombohedral: hexagonal axes; for
origin choices, origin choice 2 (nversion at the origin).

(7) Lattice parameters for the second crystal structure: see item (4)
above.

(8) The number of Wyckoff positions in the second crystal.

(9) Information about each Wyckoff position in the second crystal: see
item (6) above.

(10) Accuracy desired.  Two numbers are entered here, eps1 and eps2.
eps1 is the fractional accuracy of the lattice vectors.  For example,
eps1=0.01 means that if the two crystal are to be considered to have
the same structure, all lattice vectors must agree in length to within
1%.  The volume of the unit cell must agree to within 1.7*eps1 or, for
this example, 1.7%.

eps2 is the accuracy of the parameters x,y,z for Wyckoff positions.
For example, eps2=0.01 means that if x=0.345 in one crystal, then the
value of x must lie between 0.335 and 0.355 in the other crystal.

Standard output will repeat the input data and then will give the
following information (a copy of the output will also be written into
the file, relation.log):

(1) The relationship between the structures of the two crystals.
They may have a group-subgroup relation.  They also may have the
same structure.  Any enantiomorphic relation is also indicated.

(2) If the two crystals have related structures, the structure of the
subgroup derived from the parent is given: lattice parameters, Wyckoff
positions, lattice basis vectors of the subgroup in terms of the
lattice basis vectors of the parent, and the origin shift between the
parent and subgroup.  This information is given in the space-group
settings described in input (6) above.

More than one pair of crystals can be compared.  Simply put another
title line on the line following step (10) above.
