Configurational contributions to the free energy of embedded nanoclusters


Configurational contributions to the free energy of embedded nanoclusters

Posselt, M.; Al-Motasem, A. T.

Nanostructure evolution is a common phenomenon occurring during ion and neutron irradiation as well as during thermal treatment. It is characterized by diffusion and reaction processes that can cause the formation of embedded nanoclusters which often leads to a modification of the materials properties. Multiscale modeling can substantially contribute to a better understanding of nanostructure evolution. Atomic-scale molecular dynamics and kinetic Monte Carlo simulations are applicable on relatively small length and time scales whereas coarse-grained methods such as object kinetic Monte Carlo simulations and rate theory can be used on scales more easily accessible by experiments. The latter methods need a number of input parameters. One of the most important is the free binding energy of a monomer to a cluster which can be hardly obtained by experimental investigations but can be provided by atomistic simulations. The fundamental quantity that must be determined is the free formation energy of the clusters which consists not only of the formation energy but also of vibrational and configurational contributions. The focus of the present work is on the evaluation of the configurational part of the free formation energy. The simple example of coherent Cu nanoclusters in bcc-Fe is considered. First, at T=0 the most stable cluster configurations are determined by Metropolis Monte Carlo simulations and their formation and binding energies are calculated. Second, a modified Wang-Landau Monte Carlo method is employed in order to determine the contribution of all possible geometrical configurations of nanoclusters to the free formation energy. Finally, the total and monomer free binding energies are calculated. It is shown that even at moderate temperatures such as 600 K the configurational contributions to the free formation energy cannot be neglected. The calculation scheme applied in this work can be extended to other types of embedded nanoclusters in solids. The presented method should be especially important for nanoclusters with relatively low formation energies. Further investigations are required in order to estimate the vibrational contribution to the free formation energy and to perform a comparison with the configurational part.

Keywords: nanoclusters; free energy; configurational contributions

  • Poster
    11th International Conference on Computer Simulation of Radiation Effects in Solids, 24.-29.06.2012, Santa Fe, USA

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Publ.-Id: 17565