Symmetric Versus Nonsymmetric Structure of the Phosphorus Vacancy on   InP(110)
  The atomic and electronic structure of positively charged P vacancies on InP(110) surfaces is determined by combining scanning tunneling microscopy, photoelectron spectroscopy, and density-functional theory calculations. The vacancy exhibits a nonsymmetric rebonded atomic configuration with a charge transfer level 0.75+-0.1 eV above the valence band maximum. The scanning tunneling microscopy (STM) images show only a time average of two degenerate geometries, due to a thermal flip motion between the mirror configurations. This leads to an apparently symmetric STM image, although the ground state atomic structure is nonsymmetric. 
Ph. Ebert, K. Urban, L. Aballe, C. H. Chen, K. Horn, G. Schwarz, J.   Neugebauer and M. Scheffler