  The high solubility of oxygen in Ti, Zr and Hf makes it difficult to
stabilize the protective oxide scales on their surfaces as the subsurface
regions can serve as boundless sinks that continuously dissolve oxygen.
Alloying elements are crucial to reduce the oxygen solubility and diffusivity
within early transition metals. Past studies have shown that substitutional
alloying additions to titanium repel interstitial oxygen. Here we use
first-principles calculations to show that this repulsion is short ranged and
identify a variety of factors that are likely responsible for the repulsive
interaction. We identify a unique hybridization phenomenon between dissolved
substitutional elements and interstitial oxygen within hcp Ti that leads to a
repulsive interaction at short distances, similar to that between closed-shell
atoms. Calculations of Bader charges also suggest the existence of short-range
Coulomb interactions due to the accumulation of charge on the substitutional
solute and interstitial oxygen that is drawn from the Ti host.
