Mapping occupied space in xtal structs.

[Leonard Barbour]

Hi

Does anyone know of (IBM PC) software, either commercial or public domain, 
that will map occupied space in a unit cell?  

Given crystallographic coordinates and symmetry information, the program 
should generate grids in "slices" along a specified direction, showing 
occupied and unoccupied space as calculated using van der Waals radii.  

We currently use OPEC (Organic Packing Energy Calculations, by Gavezzotti) 
running on our VAX to do this.  However, we would like to know if any 
similar software exists.  

Typically, we would like to map the shapes of intermolecular cavities of 
host lattices in clathrates.

Thanks in advance

Len