sybyl parameters for tin disulfide



Would be grateful for suggestions on how to set the sybyl atom parameters
 for tin disulfide.  We have created the single crystal surface but we
 want to make sure the atomic radii, charge, electronegativity, etc. are
 correct to do energy minimizations of molecules on the surface.  I would
 appreciate any advice. thanks
                                  Paul Lee
                                  Dept of Chemistry
                                  Univ. of Arizona