code: public static final void shift(Structure structure, Atom a ){
  
  		AtomIterator iter = new AtomIterator(structure) ;
  		while (iter.hasNext() ) {
  			Atom atom = null ;
  
  			atom = iter.next()  ;
  
  			Atom natom = add(atom,a);
  			double x = natom.getX();
  			double y = natom.getY() ;
  			double z = natom.getZ();
  			atom.setX(x);
  			atom.setY(y);
  			atom.setZ(z);
  
  		}
  	}
docs: shift a structure with a vector.
  
  @param structure
  a Structure object
  @param a
  an Atom object representing a shift vector