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KM 1.3 - Kinetic Monte Carlo limitations One(main problem...

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University of Virginia, MSE 4270/6270: Introduction to Atomistic Simulations, Leonid Zhigilei Kinetic Monte Carlo: limitations One (main?) problem in kMC is that we have to specify all the barriers/rates in advance, before the simulation. But what if we have a continuous variation of the activation energies in the system? What if the activation energies are changing during the simulation? Example: strain on the surface can affect the diffusion of adatoms and nucleation of islands. There could be many possible origins of strain, e. g. buried islands, mesas, dislocation patterns in heteroepitaxial systems. One can try to introduce the effect of strain on the activation energies for the diffusion of adatoms. For example, Nurminen et al., Phys. Rev. B 63 , 035407, 2000, tried several approaches. In one approach, they introduced a spatial dependence of the adatom-substrate interaction on a patterned surface, E = E S (x,y) + nE N , where E is the diffusion activation energy, E S is the contribution due to the interaction with substrate, and E N is the energy of interaction with other adatoms. In another approach, an additional hop-direction dependent diffusion barrier E D is introduced to describe the long-range interaction between adatom and domain boundaries: E = E S +nE N + E D = kT t r E k T E k ) , ( exp ) , ( 0 r
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