Crystallographic symmetry interactions (e.g., packing interactions) between the molecule(s) located in the asymmetric unit and all symmetry-related molecules surrounding the asymmetric unit are computed by

where the first sum extends over all cystallographic symmetry operators () and is defined by

is the matrix that converts orthogonal coordinates into fractional
coordinates, and the second sum extends over all pairs of atoms for
which is less then a specified cutoff selected
by the constraints interaction statement
and and are the coordinates.
The function defines the minimum image distance in
fractional
coordinate space. It operates separately on each component of the
three-dimensional
vector , where the operation on each component **x** is
given by

The function is defined as the integer part of x, and is defined as the sign of x. The nonbonding interaction energy between two atoms is independent of whether it is an intermolecular or an intramolecular interaction. The atom/group search and the update of the interaction list are carried out analogously to the intramolecular case. (Refer to Section 12.3 for the definition of symmetry operators and the unit-cell constants that define .)

Sat Mar 11 09:37:37 PST 1995