Thermal Stability of Ni, Pd, and Ag Core-Shell Clusters with Bergman Geometry

This study investigates the thermal behavior of nanoalloys with a 13-atom icosahedral core surrounded by a 32-atom Bergman shell using molecular dynamics simulations. Both monometallic (Ni₁₃@Ni₃₂, Pd₁₃@Pd₃₂, Ag₁₃@Ag₃₂) and bimetallic (Ni₁₃@Ag₃₂, Ni₁₃@Pd₃₂) clusters were analyzed to evaluate the effects of atomic size mismatch and cohesive energy on melting behavior. Simulations were performed from 1 K to 1300 K under constant-temperature conditions. Caloric curves and Lindemann indices were used to identify structural transitions. Among all systems, only the Ni₁₃@Ag₃₂ cluster maintained its quasi-spherical shell integrity during heating and showed clear surface-driven melting. Other systems, including those with ideal size matching, experienced structural instabilities or rearrangements before melting. These results demonstrate that the Bergman shell offers thermal and structural stability specifically for the Ni-Ag combination, despite its moderate (~16%) size mismatch. The findings highlight the importance of both geometric compatibility and energetic favorability in the design of stable core-shell nanoalloys.