Interstitial hydrogen in bcc Nb and Ta is studied theoretically, using first-principles density-functional calculations. The effect of self-trapping is investigated in some detail, and our calculated energies, forces, and displacements for hydrogen at tetrahedral sites are all found to be in good agreement with experiments. The local motion of H and D is treated quantum mechanically by mapping out potential energy surfaces and solving a Schrödinger equation for the ground state and vibrationally excited states. Diffusion between sites is discussed in both the classical and the quantum regimes. At low temperatures, the small-polaron theory of phonon assisted tunneling is applied, and we find excellent agreement with experiments for both the calculated coincidence energy and bare tunneling matrix elements. At higher temperatures our results indicate that hydrogen migration should best be described in terms of overbarrier motion, rather than tunneling from excited states.
|Publicación||Physical Review B - Condensed Matter and Materials Physics|
|Estado||Publicada - 1 dic 2004|
Áreas temáticas de ASJC Scopus
- Materiales electrónicos, ópticos y magnéticos
- Física de la materia condensada