Subject: Crystal Packing

From: <[email-masked]>
Date: Mon, 11 Mar 1996 16:43:19 -0500 (EST)

Reply to Hiroshi Ogura:
  I am amazed at how many people have written this group in the past
few years about generating crystal structures.  Each time someone
responds with a hint about using a commercial package like Sybil or
HyperChem.
 
  I don't have access to either of these programs, so have been
working on this problems over the past few weeks.  My solution was
to take the old Oak Ridge packages like ORFEE and ORTEP and modify
them to generate any number of unit cells.  The appeal of using these
packages is that one doesn't have to reinvent any codeing for mole-
cular transformations.
  So far I have a simple FORTRAN program that takes the xyz coordinates
from a crystal paper and generates the unit cell.  For the old timers
you know that the notation for the first molecule is 55501.  If there
are 4 molecules in the unit cell, these are just specified as 55502,
55503 and 55504.  One can then move these up an axis (say b) by
just specifying 565xx, etc.  Real simple.
  My program does this and then outputs a file to BABEL.  I then
use BABEL to generate an ALCHEMY file.  I use ALCHEMY to view the
molecule.  It works.  But I can't streamline it because I don't
have the BABEL source code.  If I did, I  could compile the whole.
routine.  So there are several steps involved, but it seems to work.
  I am sure that the people with commercial packages think this is
all a waste of time.  I realize that commercial packages can generate
a unit cell from the xyz coordiates, but can they really generate
several unit cells?  This is really what's important if your looking
for nearest neighbors.  I looked at several packages that could not
determine, for example, all the atoms 4-5 Angstroms from a particular
part of any molecule.  Since ORFEE is so good at doing this, I decided
to modify the program rather that buy something that may or may not
really work.
  If this is of interest to anyone, write me and I will send you the
FORTRAN code.
  Regards, Dave Close.