Model studies of the interaction of h atoms with bcc iron |
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Authors: | Stephen P Walch |
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Institution: | Polyatomics Research Institute, 1101 San Antonio Road, Suite 420, Mountain View, California 94043, USA |
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Abstract: | Ab initio/effective core potential cluster studies are reported for the interaction of H atoms with bcc iron. The calculations use a one-electron ECP based on the 4s13d7 state of the Fe atom. Two-fold and four-fold sites on the (100) surface as well as octahedral, tetrahedral, and trigonal interior sites were studied. Four-fold surface sites are found to be bound by ~1.5 eV with the H atom ~ 0.5a0 above the surface. Penetration of the surface at a four-fold site involves movement toward a second layer atom and is expected to be unfavorable. Two-fold surface sites have small binding energies ~ 0.25 eV. Penetration of the surface at this site involves movement toward a tetrahedral interior site and is downhill in energy. Tetrahedral interior sites are found to be bound by ~1.3 eV and are a minimum on the potential energy surface. Octahedral sites are a maximum on the potential energy surface and are estimated to be ~ 0.2 eV higher (including lattice relaxation effects). Trigonal sites are found to be a saddle point connecting adjacent tetrahedral sites and this pathway leads to an estimated barrier to diffusion of ~ 0.1 eV (including lattice relaxation effects). The volume expansion for a H atom in a tetrahedral site is calculated to be 21%. |
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