  Based on first-principles simulations, the structural stability and magnetic
uniformity of Pt13 nanoparticles encapsulated in a NaY zeolite were
investigated. Among 50 stable isomers in the gas phase, only 15 could be
accommodated into a zeolite pore and severe structural rearrangements occured
depending on whether the solid angle at the Pt vertex bound to the supercage
was larger than 2 sr (i.e. icosahedron). When van der Waals forces were
included, the global minimum was found to be a new L-shaped cubic wire that is
unstable in the gas phase. The total magnetization of the encapsulated Pt13
decreases due to the stabilization of less coordinated isomers, with the
majority of clusters charaterized by a total magnetization of 2 {\mu}B, while
the majority of free clusters exhibit a threefold value.
