Theory of the heat of solution of hydrogen in Al and Mg using nonlinear screening

A theory of the heat of solution of hydrogen in simple metals is developed and results are presented for the cases of aluminum and magnesium. The electronic contribution to the heat of solution is treated within the framework of local pseudopotential theory and is based on linear screening. For the proton contribution it is necessary to use nonlinear theory for the screening of the proton and a convenient framework for this is the density functional formalism with exchange and correlation corrections included approximately. The calculated value of the heat of solution for aluminum is 0.45 eV which compares favorably with the experimental value of 0.66 eV. The result for magnesium, -0.05 eV, is also in reasonable agreement with the experimental value of 0.25 eV bearing in mind that the hydrogen heat of solution is obtained as the difference of two energies of about 15 eV. The energy has also been investigated as a function of the position of the proton in the lattice. Calculated energy barriers are used to estimate proton diffusion parameters.