  Band alignment between solids is a crucial issue in condensed matter physics
and electronic devices. Although the XPS method has been used as a routine
method for determination of the band alignment, the theoretical calculations by
copying the XPS band alignment procedure usually fail to match the measured
results. In this work, a reliable ab-initio calculation method for band
alignment is proposed on the basis of the XPS procedure and in consideration of
surface polarity and lattice deformation. Application of our method to anatase
and rutile TiO2 shows well agreement between calculation and experiment.
Furthermore, our method can produce two types of band alignment: the coupled
and the intrinsic, depending on whether the solid/solid interface effect is
involved or not. The coupled and intrinsic band alignments correspond to
alignments measured by XPS and electrochemical impedance analysis,
respectively, explaining why band alignments reported by these two experiments
are rather inconsistent.
