Force field parameters around Au atom that have been lacking in standard parameter set of the MMFF94s were temporarily determined to reproduce the molecular crystal structure of phenyl(phenylisocyanide)gold(I) complex by classical force field calculations. It was confirmed that two polymorphic forms optimized by CONFLEX software with these parameters are in good agreement with the experimental structures. Application of the parameters to other derivatives also gives good results but the Au..Au distances in some crystal structures are longer than those of the experimental. Therefore, further optimization of these parameters will be required.