Multilayer relaxation of body-centred-cubic Fe(211)

The atomic structure of the clean surface of BCC Fe(211) was analysed by low-energy electron diffraction (LEED). Thirty intensity-energy spectra (19 non-equivalent) for three directions of incidence were collected and compared with calculations by means of a reliability factor. The surface structure consists of a first-layer registry shift of 0.24+or-0.03 AA with respect to the second layer, a second-layer registry shift of 0.037+or-0.03 AA with respect to the third layer in the direction opposite to the first-layer registry shift, a first interlayer spacing d₁₂=1.05+or-0.03 AA (bulk value is 1.17 AA), a second interlayer spacing d₂₃=1.23+or-0.03 AA and a third interlayer spacing d₃₄=1.15+or-0.04 AA. The first-layer registry shift is along a (111) direction such as to decrease the difference between nearest and next-nearest neighbour bond lengths among atoms in the top two layers. The overall agreement between theory and experiment as measured by the reliability factor of Zanazzi and Jona (1977) is 0.111.