code: private IAtomType getAtomType(String ID) throws NoSuchAtomTypeException {
          IAtomType at = null;
          for (int i = 0; i < atomTypes.size(); i++) {
              at = (IAtomType) atomTypes.get(i);
              if (at.getAtomTypeName().equals(ID)) {
                  return at;
              }
          }
          throw new NoSuchAtomTypeException("AtomType " + ID + " could not be found");
      }
docs: Find the atomType for a id
  
  @param  ID                           Atomtype id of the forcefield
  @return                              The atomType
  @exception  NoSuchAtomTypeException  atomType is not known.