T
he relative stability of multiferroic BiFeO
3 (0001) surfaces, which is t
he (111) facet in t
he pseudocubic notation, with different stoichiometry is systematically studied by using
ab initio t
hermodynamic approach in order to obtain insights into t
he stable surface terminations. We predict that under most c
hemical potential conditions t
he t
hermodynamically favored terminations for t
he negative and positive surfaces are −Bi–O
2 and −Fe–O
3–Bi, respectively. T
he predicted difference in oxygen content between t
he negative and positive surfaces is consistent with experimental observations at t
he BiFeO
3/metal interfaces (
Nat. Mater.,
hema-instance" xml:space="preserve"> 2014
hema-instance" xml:space="preserve">, 13hema-instance" xml:space="preserve">, 1019, DOI:
10.1038/nmat4058; Adv. Mater.,hema-instance" xml:space="preserve"> 2015hema-instance" xml:space="preserve">, 27hema-instance" xml:space="preserve">, 6934, DOI: 10.1002/adma.201502754). We determine the atomic geometries and electronic states as well as the magnetic properties for the negatively and positively polarized stable surfaces. Our results demonstrate that not only the stoichiometry and atomic geometries but also the electronic and magnetic properties of the BiFeO3 (0001) surfaces show strong dependence on the ferroelectric polarization direction. Therefore, we expect that the surface physical and chemical properties of the BiFeO3 (0001) surfaces can be easily tuned by an external electric field.