  Numerous different crystal structures of Ta2O5 are reported in literature.
Although experimentally and computationally obtained lattice parameters and
mechanical properties are in excellent agreement there is a pronounced
deviation when it comes to electronic structures of Ta2O5. Based on ab initio
studies and nano-beam X-ray diffraction of sputtered Ta2O5 thin films, we
introduce an orthorhombic basic structure with a = 0.6425, b = 0.3769, and c =
0.7706 nm, which is stabilized by flipping of an oxygen atom in neighboring
c-planes. The calculated energy of formation is with -3.209 eV/atom almost as
low as -3.259 eV/atom for the well-known Stephenson superstructure. We propose
the new structure based on the fact that it allows for a good description of
orthorhombic Ta2O5 even with a small and simple unit cell, which is especially
advantageous for computational studies.
