  The lattice relaxation in oxygen-deficient Ta2O5 is investigated using
first-principles calculations. The presence of a charge-neutral oxygen vacancy
can result in a long-ranged lattice relaxation which extends beyond 18 {\AA}
from the vacancy site. The lattice relaxation has significant effects on the
vacancy formation energy as well as the electronic structures. The long-ranged
behavior of the lattice relaxation is explained in terms of the
Hellmann-Feynman forces and the potential energy surface related to the
variation of Ta-O bond lengths.
