  Within the harmonic approximation, the effects of lattice vibration on the
thermodynamics of nano-sized coherent clusters in bcc-Fe consisting of
vacancies and/or copper are investigated. A combination of on-lattice simulated
annealing based on Metropolis Monte Carlo simulations and off-lattice
relaxation by Molecular Dynamics is applied to obtain the most stable cluster
configurations at T = 0 K. The most recent interatomic potential built within
the framework of the embedded atom method for the Fe-Cu system is used. The
vibrational part of the total free energy of defect clusters in bcc-Fe is
calculated using their phonon density of states. The total free energy of pure
bcc-Fe and fcc-Cu as well as the total formation free energy and the total
binding free energy of the vacancy-copper clusters are determined for finite
temperatures. Our results are compared with the available data from previous
investigations performed using empirical many-body interatomic potentials and
first-principle methods. For further applications in rate theory and object
kinetic Monte Carlo simulations, the vibrational effects evaluated in the
present study are included in the previously derived analytical fits based on
the classical capillary model.
