The three-adatom non-pairwise (“trio”) interaction,with implications for Monte Carlo simulations of O/W(110)

Ching et al.¹ found that three-adatom non-pairwise interactions, with a repulsive energy greater than a quarter the nearest pair attraction, can explain the pronounced asymmetries in the phase diagram of O/W(110). In the first explicit calculations of such short-range “trio” interactions, we find that electronic indirect interactions have strengths consistent with their parameters. In general the closest-spaced trios are stronger than all but the few shortest-range pair interactions which determine the adlayer symmetry. We further show that triad configurations with similar shorter legs should have comparable magnitude; when applied to O/W(110), this idea doubles the number of trios entering the equations of Ching et al.¹ and thus can halve the minimum required trio strength. Such trio interactions (as well as linear triad configurations) have a substantial quantitative effect on the pair interaction strengths extracted from Monte Carlo simulations.