Computer simulations of crystal growth defects

in highly supersaturated solutions, potassium dichromate crystals exhibit a growth anomaly on (00 (1) over bar): this face is rough and covered by man y potassium dichromate platelets that are only a few mu m thick. even thoug h the structure is centrosymmetric. The following study is based on the crystallite orientation and dichromate classification. The force field method showed that intergrowths of complete structural unit s (crystal nuclei) in the twin position are energetically favourable on (00 (1) over bar) but not on the symmetrically equivalent (001) face. The ener getically favourable intergrowth laws occur in nature as macroscopic twins. The necessary potential parameters were determined using a combination of empirical fitting, quantum mechanical ab initio calculations, and normal co ordinate analysis of the vibration spectra. The empirical fitting was prefo rmed using GULP program.