Change of ground state configuration induced by the Stark shift of surface states in some bcc(001) surfaces

Using density functional calculations, we found that the ground state configuration of some bcc(001) surfaces are field dependent because different configurations experience different Stark shifts of surface states. When the W(001) surface is positively biased, an external electric field stabilizes a c(2 x 2) array of surface vacancies, so that the ground state is no longer the well-established "Debe-King" model. Similar behavior is found for Mo(001), but not for Nb(001). The field-induced change of ground state provides a natural explanation for the anomalous behavior of W(001) inside field ion microscopes. [S0031-9007(99)08932-2].