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548. PCK83: A Crystal Molecular Packing Analysis Program
(IBM 3090 Version)
by Donald E. Williams, Department of Chemistry,
University of Louisville, Louisville, Kentucky 40292
Converted by W. Hwung, Department of Chemistry, Indiana
University, Bloomington, Indiana 47405
This program has been vectorized for use on the IBM
3090 with Vector Facility and makes extensive use of
the ESSL (Engineering and Scientific Subroutine
Library).
PCK83 calculates crystal lattice energies of molecular
crystals and finds crystal structures with minimum
energy. Usually, the molecule is considered to be
rigid, but limited provisions are made for internal
rotations about bonds. The general procedures used are
presented in a paper published in Acta
Crystallographica, A28, 629-635 (1972). A recent
review appears in Topics in Current Physics, 26, 3-40
(1981). An earlier version of this program was called
PCK6 and was listed as QCPE 373 (1979).
The intermolecular or nonbonded energy of the crystal
is represented by a pairwise sum over atoms in
different molecules. The program accepts either (exp-
6-1) or (n-6-1) non-bonded interatomic potentials
(referred to as Buckingham or Lennard-Jones functions).
A torsional potential is accepted for rotations about
internal bonds. Provision is made for net atomic
charges or lone-pair electron-site charges. The
structural variables considered by the program are the
six lattice constants, three molecular rotations, three
molecular translations, and internal rotations. An
external hydrostatic pressure on the crystal may be
included.
Calculations can be made with the observed space-group
symmetry or with no assumed symmetry. The energy and
structure of molecular clusters can be calculated.
There can be more than one independent molecule in the
crystallographic asymmetric unit. Evaluation of the
crystal lattice sums uses the accelerated convergence
method (Acta Crystallographica, A27, 452 (1971)) so
that high speed and accuracy can be obtained. The
first and second derivatives of the lattice energy are
evaluated
analytically, also using accelerated convergence. The
program selects the Newton-Raphson method to find the
calculated structure with minimum energy if the
eigenvalues of the Hessian (second derivative) matrix
are positive-definite; otherwise, the steepest descent
method is used.
IBM FORTRAN (Version 2.2 PUT 8801)
Lines of Code: 3563
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