Hydrogen absorption in face-centered-cubic palladium was studied from first principles, with particular focus on interaction between hydrogen atoms and vacancies, formation of hydrogen-vacancy complexes, and multiple hydrogen occupancy of a Pd vacancy. Vacancy formation energy in the presence of hydrogen, hydrogen trapping energy, and vacancy formation volume were calculated and compared to existing experimental data. It was shown that a vacancy and hydrogen atoms form stable complexes. Furthermore, a study was made of the process of hydrogen diffusion into the Pd vacancy. It was found that the energetically preferable position for hydrogen was to reside in the palladium unit cell in the presence of a vacancy. The possibility of the multiple hydrogen occupancy (up to six hydrogen atoms) of a monovacancy was elucidated. This theoretical finding supports experimental indication of the appearance of superabundant vacancy complexes in palladium in the presence of hydrogen.

First-Principles Study of Vacancy-Hydrogen Interaction in Pd. O.Y.Vekilova, D.I.Bazhanov, S.I.Simak, I.A.Abrikosov: Physical Review B, 2009, 80[2], 024101