SURFACE EFFECTIVE-PAIR INTERACTIONS IN A MODEL TRANSITION-METAL ALLOY

For a model transition-metal alloy, we find that changes in the third and fourth moments of the electronic density of states alter the effec tive-pair interaction (EPI) ordering range. The EPI dependence on conc entration, single-site energy, and crystal face is explained by showin g the dependence of the state-density third and fourth moments on thes e variables. Examples illustrating these effects are given for bcc and fcc surface EPI's. From this analysis, we find that bulk-clustering a nd surface-ordering behavior is more likely than bulk-ordering and sur face-clustering behavior. In addition, we find that the presence of br oken bonds tends to increase the ordering range.