  The structure, dynamics and stability of Fe-Pt nanoparticles have been
investigated using DFT-based techniques: total energy calculations and DFT
molecular dynamics. The investigated systems included multi-shell and
disordered nanoparticles of iron and platinum. The study is concerned with
icosahedral particles with magic number of atoms (55): iron-terminated
Fe$_{43}$Pt$_{12}$, platinum-terminated Fe$_{12}$Pt$_{43}$, and disordered
Fe$_{27}$Pt$_{28}$. Additionally, the Fe$_6$Pt$_7$ cluster has been
investigated to probe behaviour of extremely small Fe-Pt particles. Molecular
dynamics simulations have been performed for a few temperatures between
$T=150-1000$ K. The calculations revealed high structural instability of the
Fe-terminated nanoparticles and a strong stabilising effect of the
Pt-termination in the shell-type icosahedral particles. The platinum
termination prevented disordering of the particle even at $T=1000$ K indicating
very high melting temperatures of these Fe-Pt icosahedral structures. The
analysis of evolution of the radial distribution function has shown significant
tendency of Pt atoms to move to the outside layer of the particles -- even in
the platinum deficient cases.
