code: public void addAtoms(Atom[] iAtoms, Atom[] jAtoms) {
  		addAtoms(iAtoms, null, jAtoms, null);
  	}
docs: Adds the i and j atoms and fills the grid. Their bounds will be computed.
  Subsequent call to {@link #getIndicesContacts()} or {@link #getAtomContacts()} will produce the interatomic contacts.
  @param iAtoms
  @param jAtoms