code: public static final double scalarProduct(Atom a, Atom b) {
  		return a.getX() * b.getX() + a.getY() * b.getY() + a.getZ() * b.getZ();
  	}
docs: Scalar product (dot product).
  
  @param a
  an Atom object
  @param b
  an Atom object
  @return a double