(defmethod move-to ((atom cqm-atom) &rest r)
  (cond ((eql (list-length r) 1) ; r is a list of one vector-3d object
     (setf (location atom) (nth 0 r)))
    ((eql (list-length r) 3) ; r is a list of three cortesian coordnates x, y and z
     (let ((x (nth 0 r)) (y (nth 1 r)) (z (nth 2 r)))
       (setf (location atom) (make-instance 'vector-3d :x x :y y :z z))))))