code: public static final Atom getCenterVector(Atom[] atomSet, Atom centroid){
  
  		double[] coords = new double[3];
  		coords[0] = 0 - centroid.getX();
  		coords[1] = 0 - centroid.getY();
  		coords[2] = 0 - centroid.getZ();
  
  		Atom shiftVec = new AtomImpl();
  		shiftVec.setCoords(coords);
  		return shiftVec;
  
  	}
docs: Returns the Vector that needs to be applied to shift a set of atoms to
  the Centroid, if the centroid is already known
  
  @param atomSet
  array of Atoms
  @return the vector needed to shift the set of atoms to its geometric
  center