Electronic structure study of scanning tunneling microscopy images of the rutile TiO2(1 1 0) surface and their implications on the surface relaxation

In scanning tunneling microscopy (STM) images recorded for rutile TiO2(1 1 0) surfaces with oxygen vacancies, the non-defect-site five-coordinate Ti atoms and the vacancy sites of the bridging oxygen atom rows appear bright while the six-coordinate Ti atoms and the bridging oxygen atoms appear dark. To find what kinds of surface relaxation can cause such STM images, we carried out partial density plot calculations for the unrelaxed structure and a number of model relaxed structures of the rutile TiO2(1 1 0) surface with oxygen vacancies using the extended Hückel tight binding method. We also performed density functional theory calculations to estimate the Ti atom displacements for the three types of Ti atoms present on TiO2(1 1 0) surfaces with oxygen vacancies.