The structural and dynamical properties of FePt nanoparticles were studied
within the density functional theory. The effect of size and chemical
composition on dynamical stability of nanoparticles was investigated for the
cuboctahedral and icosahedral symmetries. In cuboctahedra, the structural
distortion is observed, which for systems with odd number of Pt layers leads to
lowering of the tetragonal symmetry. Significant differences between the
vibrational properties of FePt particles and bulk crystal is observed, but
similarly to the FePt crystal, cuboctahedral particles exhibit a strong
anisotropy of atomic vibrations. The icosahedral particles with perfect shell
geometry are unstable due to enlarged distances between Fe atoms. They can be
stabilized by removing a central atom or replacing it by a smaller one. The
heat capacity and entropy of nanoparticles show typical enhancement due to
low-energy vibrations at the surface layers.Comment: 10 pages, 14 figures, 2 tables, accepted in Phys. Rev.