It was noted that, in various situations, the vacancy-adatom pair was the most widely spread defect on low-index surfaces; due to its appreciable contribution to the entropy of adatom positions. The results of calculations, performed using embedded-atom methods, showed that the formation energy of the vacancy-adatom pair was slightly less than, or equal to, that of the vacancy in most of the cases which were considered.

Point Defects at Low-Index Surfaces of FCC Metals - Formation Energies of Vacancies and Adatom-Vacancy Pairs. Y.N.Devyatko, S.V.Rogozhkin, A.V.Fadeev: Physical Review B, 2001, 63[19], 193401 (4pp)