Issues in the ab-initio assessment of hcp transition metals self-diffusion

Abstract

Electronic structure techniques,asembodied in the SIESTA code, are presently used for assessing self-diffusion in the hcp transition metals Zr and Ti. Several issues pertaining to this apparently hard caseand not routinely found in the literature, are touched upon, a partial list including: (i) the suitability of available pseudopotentials, (ii) the need to employ fine space grids for the numerical integrations, (iii) the need of a rather large basis set, (iv) the reliability of the simulation cell size and boundary conditions, etc. All of which affect the precision of the magnitudes to be evaluated, namely, in theframe work of transition state theory and assuming a standard vacancy mechanism, formation energyand entropy, migration energies, and attempt frequencies.