Browsing by Subject "Nudged Elastic Band"

The diffusion of a single hydrogen atom through solid tungsten was studied using two separate computational methods: Molecular dynamics simulations and nudged elastic band calculations. Molecular dynamics was used to track the atom’s path in the tungsten lattice in several successive simulations to obtain its mean squared displacement. Results were obtained for temperatures between 400 K and 700 K. These were used to derive a temperature relation for the diffusion coefficient and an estimate for the diffusion energy barrier, which was 0.1985 eV. The nudged elastic band method was used to directly obtain an estimate for the diffusion energy barrier. The same tungsten lattice system as in the molecular dynamics simulations had the hydrogen atom relaxed into an interstitial position and then moved over the energy barrier into an adjacent site. If the tungsten atoms were allowed to relax during the motion, a comparable value of 0.2022 eV was obtained. Further computations were made with a fixed-length tungsten bond next to the hydrogen starting position, yielding energy barriers from 0.1 eV to 1.2 eV depending on the bond length, direction of the diffusion jump and tungsten relaxation. In conclusion, the two different computational methods do give results for the energy barrier that are comparable in magnitude, but further measurement of the tungsten bonds near the hydrogen atom during the molecular dynamics simulation may be needed for a more matching comparison from the nudged elastic band results.