I have not studied any chemistry or physics beyond early years, but I am not aware of any reason to believe that any parametric approach would be reasonable, whereas polynomial approaches (including many kinds of transformations, etc.) have been successful in answering a great diversity of natural phenomena. I wouldn't think parametric unless a) there was a specific theoretical reason to believe it should be parametric, or b) there is specific empirical complications/refutations in establishing a specifically polynomial approach.