Solution enthalpy of hydrogen in fourth row elements: Systematic trends derived from first principles

Based on first-principles calculations, we identify a master curve for the solution enthalpy of H in fourth row elements including all $3d$ transition metals. Assuming nonmagnetic fcc crystal structures, we find two different classes of materials with either the octahedral or the tetrahedral interstitial site being preferred by hydrogen. An interaction radius for H in octahedral site of ≈0.7 {} (≈0.4{} for H in tetrahedral site) turns out to be a characteristic value for which the chemical interaction energy has an optimum for all studied elements.