The symbol must be be unique. The cutoff distance for loop closing bonds which cannot be defined by the tree structure. Any pair of atoms within this distance is assumed to be bonded. We recommend that CUT be set to 0.0 and explicit loop closing bonds be defined below. The actual number of the atom in the tree.
PREP always expects three dummy atoms for the beginning.
If coordinates are read in at the EDIT stage, this name will be used for matching atoms. Maximum 4 characters. A symbol for the atom I which defines its force field atom type and is used in the module PARM for assigning the force field parameters. The atom number to which atom I is connected. If cartesian coordinates are used, this must be omitted.