  Oxygen greatly affects the mechanical properties of titanium. In addition,
dislocations and twin boundaries influence the plastics deformation of hcp
metals. As part of a systematic study of defects interactions in Ti, we
investigate the interactions of oxygen with (10-12) twin boundary and (10-10)
prism plane stacking fault. The energetics of four interstitial sites in the
twin geometry are compared with the bulk octahedral site. We show that two of
these sites located at the twin boundary are more attractive to oxygen than
bulk while the sites away from the boundary are repulsive. Moreover, we study
the interaction of oxygen with the prismatic stacking fault to approximate
oxygen-dislocation interaction. We show that oxygen increases the stacking
fault energy and therefore is repelled by the faulted geometry and consequently
a dislocation core.
