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373. PCK5/PCK6: Molecular Packing Analysis in Crystals
by Donald E. Williams, Department of Chemistry,
University of Louisville, Louisville, Kentucky 40208
The crystal lattice energy is minimized by the least-
squares, Newton-Raphson, or steepest-descent method as
a function of the structural parameters.The
simplified program, PCK5, uses the observed lattice
constants and finds the optimum rotational and
translational positions of the molecules in the cell.
Quadratic nonbonded potentials are used with least
squares minimization.
The larger program, PCK6, includes the lattice
constants as variables and allows intramolecular
rotations about bonds. The nonbonded potentials are of
the (exp-6-1) type, plus internal rotation potentials.
Accelerated convergence of the lattice sums is used.
Refinement proceeds via steepest descents, switching to
Newton-Raphson as permitted.
The program is dimensioned for 100 atoms in the
asymmetric unit, including hydrogens (easily changed);
less than 32 Kb word storage is required.
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References:
PCK5:D. E. Williams, "A Method of Calculating
Molecular Crystal Structures," Acta Cryst., A25,
464 (1969).
PCK6:D. E. Williams, "Molecular Packing Analysis,"
Acta Cryst., A28, 629 (1972).
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FORTRAN IV
Lines of Code: 4072
Recommended Citation: D. E. Williams, QCPE 11, 373
(1979).
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