Boreskov Institute of Catalysis of the Siberian Branch of Russian ...

OP-II-2gas model use, there is no need to support dynamic lists of neighbour atoms, but similar listscan be prepared before simulation for each lattice cell and such lists don’t need to berefreshed during simulation. No suggestions about lattice type are made by the simulationalgorithm, so the model easily can be adopted for any kind of crystal.On attempt to execute a diffusion act an atom isselected from the list of lattice cells with activeatoms (atoms of the particle which can take part indiffusion process). This list is dynamically updatedon each successful diffusion act and is in actual stateduring the whole simulation. The second lattice cellis picked from the neighbor list of the first one andan attempt to change their content is being doneSupported Pt particle with atoms adsorbedon (111) faceaccording to Boltzmann distribution. This approachgives higher acceptance rate than mathematical diffusion because amount of unlikely jumpsfrom the middle of the particle to a free space is reduced. Also in that way the system reachesan equilibrium state in a less amount of steps in comparison with realistic diffusion.An adsorbed atom forms some spatial configuration with adsorbent atoms. Set of suchconfigurations defines adsorption type. It can be adsorption on top, on bridge, on hollow sites,on three or four atoms, on steps or other defects. For our model this set can be specified ininternal coordinates. For each given configuration a lattice pattern is being built for allpossible orientations in space. Obtained patterns can be effectively matched against thelattice. It allows quick search of places on the simulated particle which are suitable for somekind of adsorption. Adsorbed atoms don’t have to be placed in lattice cells, their position isdetermined by vector beginning form some lattice cell. Length of this vector is comparablewith distance between atoms in the crystal. Therefore a list of adjacent adsorbed atoms can bebuild by enumeration of neighbor lattice cells which, as described above, can be done quickly.SimulationsWe have used this model for adsorption simulation on supported Pt nanoparticles withdifferent values of pressure and parameters of interaction between the particle and adsorbate.An influence of adsorption on particle form has been investigated.References1. V.I. Elokhin and A.V. Myshlyavtsev, Catalytic Processes over Supported Nanoparticles: Simulations, inDekker Encyclopedia of Nanoscience and Nanotechnology, ed. Taylor & Francis, 2004.2. F. Cleri and V. Rosato Phys. Rev. B., 1993, 48, 22-33.78