Dear Fen Hong,I think you should fix only one axis of the gold atoms, as it is expected that the molecule has at least some influence on the surface spot where it connects. So it might be better for the in-plane movement to be not totally fixed. But you have to decide whether you want to include this interaction or not.
Good Luck and Best Regards Heiko -- Heiko Dumlich Freie Universität Berlin Fachbereich Physik - AG Reich Arnimallee 14 D-14195 Berlin GERMANY Phone: +49-30-838 56157
