  The shape memory behavior of a NiTi nanoparticle is analyzed by molecular
dynamics simulations. After a detailed description of the equilibrium
structures of the used model potential, the multi variant martensitic ground
state, which depends on the geometry of the particle, is discussed. Tensile
load is applied, changing the variant configuration to a single domain state
with a remanent strain after unloading. Heating the particle leads to a shape
memory effect without a phase transition to the austenite, but by variant
reorientation and twin boundary formation at a certain temperature. These
processes are described by stress-strain and strain-temperature curves,
together with a visualization of the microstructure of the nanoparticle.
Results are presented for five different Ni concentrations in the vicinity of
50%, showing for example, that small deviations from this ideal composition can
influence the critical temperature for shape recovery significantly.
