Dear All, I am very sorry to involve you into such insignificance discussion, I have reached agreement with Prof Gerard, please stop talking about things beyond science, thanks! I read a book today, which said "A refined model should exhibit rms deviations of no more than 0.02A for bond length and 4 for bond angels", I just wonder about the standard of the bond length and the bond angel. I think most of you have read similar words! But maybe I didnot express clearly and made some phrasal mistakes. At last, happy new year to you all--though very late! Sincerely! Yang Li