A detailed  ab initio  total energy minimization study was made of As vacancies, VAs, in the (110) surface. Previous scanning tunnelling microscopic images of VAs in p-type (110) were explained in terms of a structure which involved an outward movement of the Ga atoms next to the vacancy. Simulations of scanning tunnelling microscopic images, performed using  ab initio  wave functions, agreed with experimental data. However, total energy minimization results suggested the occurrence of an inward movement of the Ga atoms. This discrepancy was explained in terms of a charge-induced band-bending effect. It was therefore predicted that the scanning tunnelling microscopic images depended upon the applied bias voltage. It was shown that the atomic geometry of the surface VAs depended critically upon the charge state. This was very different to the behavior of the bulk vacancy.

S.B.Zhang, A.Zunger: Physical Review Letters, 1996, 77[1], 119-22