PSI - Issue 68

D.M. Tshwane et al. / Procedia Structural Integrity 68 (2025) 39–46 D.M. Tshwane et al. / Structural Integrity Procedia 00 (2025) 000–000

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the HE characteristics. The interaction strength and hydrogen reaction on the Ti 2 AlV surface are analysed by adsorption energies, work function, density of states, Mulliken charge population, and charge density difference. Hydrogen adsorption energy is a crucial factor in determining the strength of its interaction with metal atoms. These findings can provide notable insights on the adsorption of hydrogen on Ti 2 AlV surface, offering atomic level evidence for the mechanisms underlying the hydrogen embrittle. 2. Computational method All DFT calculations were carried out using the plane-wave pseudopotential method implemented in the Cambridge Sequential Total Energy Package (CASTEP) code (Segall et al., 2002). A generalized gradient approximation of Perdew-Burke-Ernzerhof (PBE) was used to explain the energy of the exchange-correlation interaction (Perdew et al., 1996). A complete structural optimization and energy minimization calculation was performed with cutoff energy and Monkhorst-Pack k-points of 500 eV and 4x4x1, respectively (Monkhorst and Pack, 1976). Geometry optimization was performed using the Broyden-Fetcher-Goldforb-Shanno (BFGS) minimization scheme technique. The absolute maximum force and the convergence tolerance were set at 0.03 eV/Å and 10 −5 eV/atom, respectively. DFT-D method developed by Grimme et al. (2011) was employed to correct the effect of vdW interactions for evaluating the adsorption energies. Both the adsorbent (Ti 2 AlV surface) and the adsorbate (hydrogen) were allowed to relax in order to examine the stability of adsorption. The definition of the adsorption energy is given by: !"# = $/#&'( − $ $ + #&'( & (1) The terms $/#&'( , $ and #&'( refer to the total energy of the Ti 2 AlV surface, the surface-free H atom, and the pure Ti 2 AlV surface (110), respectively. The lowest adsorption energy value (negative) implies that hydrogen adsorption is preferential (more stable), whereas the highest value suggests less preferential adsorption (less stable). The atomic schematic representations of bulk Ti 2 AlV and Ti 2 AlV (110) surface structures are shown in Fig. 1. Ti 2 AlV (110) surface structure was created using the optimized and stable bulk Ti 2 AlV. Previous research has reported on the structural and thermodynamic stability of Ti 2 AlV (110) in both its bulk and surface structures (Tshwane and Modiba, 2022a, 2022b).

Fig. 1. Atomic schematic representations of (a) bulk Ti 2 AlV and (b) Ti 2 AlV (110) surface model structures.