When Pt adatom transit from one four-fold site to another, the energy for it being reactant should be the same as it being the product.

So the height is tuned manually by putting the adatom between 1Å to 3Å above the center of the four-fold site. Consider the short range dispersion, there should be a local energy minimum for the Pt to sit on top of the surface and bring down the system’s energy. Sitting on top of the fourfold site, it is obvious that the adatom cannot be either too close or too far from the surface where too close to each other there will be repulsion and too far to each other will make Pt adatom isolated from the surface and could interact with the next periodic slab. To do this, one will first identify the most stable height of the Pt adatom on the surface. Use the lowest energy vacuum space to continue slab size optimization. Example of the slab used for vacuum space optimization. Layers of the slab will not be optimized due to time limit, and based upon experience, five layers should be enough.įor vacuum space optimization, build three slabs with 5Å, 10Å and 15Å vacuum space, and calculate energy with CASTEP, functional used is GGA PBE, pseudo-potential is OTFG-ultrasoft, and all other parameters are set to default (272.1eV energy cutoff, 6 圆x1 K-points, core radii is 1.27A with electron configuration to be 5s2 5p6 5d9 and 6s1).įigure 1. As mentioned the goal of the experiment is to identify the more likely transition process from the two, and in order to get reasonable comparison between the two processes, one need to first optimized the system(slab) to make sure that the super-cell is large enough for boundary conditions and enough vacuum space to prevent interaction from the next periodic slab along the Z-axis. Experimental:įirst cleave the Pt(100) lattice, and create the slab and a five-layer slab of 2X2 super-cell with 5Å vacuum space was set as the starting point. By connecting the initial and final state of the system, one could locate the TS (transition state) of that process and use the energy barrier from the transition search to further study the kinetic of process. To study the process, a model needs to be built and in our case the model is fairly simple since neither diffusion process has linear interpolation issue, and as consequence, one just need an initial and final two-state model for the transition state study. In our case, Pt adatom is hypothesized to undergo a hopping between two adjacent four-fold sites or undergoes concerted substitution. Diffusion is governed by the thermal energy from the environment and the property of such behavior is important for understanding surface phase formation, heterogeneous catalysis and other aspects. Surface diffusion is a common process for solid materials, and in our case, the Pt adatom could diffuse along the surface of Pt(100).

Cleaving hcp in materials studio