Dear Pwscf Users, I have started using CI NEB method implemented in espresso. I deal with native defects in bulk materials; let's say Cd interstitial in CdTe, which crystalizes in zinc blende structure. It is known that it diffuses along [111] direction between tetrahedral sites.
Previously, to calculate barriers for diffusion I used 'direct' approach (I coined this name), which means I calculated total energies by fixing the position of an interstitial at a number of sites between metastable sites, and allowing all other atoms to relax (except one located at the outskirts of supercell, i. e., far away form the defect). The barriers heights calculated using NEB are usually higher than those obtained by 'direct' approach. I try to understand these differences. Because the diffusion occurs along [111] direction in straight line, so the path is to some extent in this case trivial (I am stressing it, because it is ok to choose nstep=1 in neb). Is there a clear, unanimous explanation why it is so? Are you familiarized with any paper in literature giving discussion of the dicrepancies between NEB results and those obtained using 'direct' approach? What is the physics behind it? Thank you very much in advance for any comments, hints and help. Pawel Jakubas PhD Student Piotr Boguslawski Group Institute of Physics Polish Academy of Sciences AL. Lotnikow 32/46 PL-02-668 Warsaw, POLAND group webpage: http://www.ifpan.edu.pl/SL-3/ my webpage: http://www.ifpan.edu.pl/SL-3/PJakubas/jakubas.html
