  Titanium borates show promissing hydrogen storage characteristics. Structural
relaxation around individual hydrogen atoms and the binding energies are
studied by means of the density functional theory methods for a number of
hydrogenated TiB2, TiB and Ti2B structures. Starting with the possible
symmetric hydrogen sites a random structure searching has been performed, in
addition to locate all energetically stable adsorption sites. It is shown that
for the three bulk compounds considered, the lowest binding energies are
obtained for TiB2 (in the 0.3-1.8 eV range), the largest for Ti2B (in the
3.9-4.7 eV range), while for TiB they are intermediate (in the 2.8-3.5 eV
range). Calculations performed on hydrogenated Ti2B result in two energetically
stable sites for two different starting environments, suggesting a posible soft
mode solution.
