# Chemical Orderings in CuCo Nanoparticles: Topological Modeling Using DFT Calculations

## TL;DR

This paper studies how copper and cobalt atoms arrange in small nanoparticles and how CO molecules affect their structure and properties.

## Contribution

A novel topological approach combined with DFT calculations is used to model CuCo nanoparticle orderings and CO adsorption effects.

## Key findings

- Cu atoms prefer surface positions while Co atoms cluster internally in CuCo nanoparticles.
- CO adsorption at low coverage can displace Co clusters within Cu matrices.
- CO adsorption energy and vibrational frequencies can indicate active surface sites in CuCo nanoparticles.

## Abstract

The orderings of atoms in bimetallic 1.6–2.1 nm-large CuCo nanoparticles, important as catalytic and magnetic materials, were studied using a combination of DFT calculations with a topological approach. The structure and magnetism of Cu50Co151, Cu101Co100, Cu151Co50, and Cu303Co102 nanoparticles; their resistance to disintegrating into separate Cu and Co species; as well as the exposed surface sites, were quantified and analyzed, showing a clear preference for Cu atoms to occupy surface positions while the Co atoms tended to form a compact cluster in the interior of the nanoparticles. The surface segregation of Co atoms that are encapsulated by less-active Cu atoms, induced by the adsorption of CO molecules, was already enabled at a low coverage of adsorbed CO, providing the energy required to displace the entire compact Co species inside the Cu matrices due to a notable adsorption preference of CO for the Co sites over the Cu ones. The calculated adsorption energies and vibrational frequencies of adsorbed CO should be helpful indicators for experimentally monitoring the nature of the surface sites of CuCo nanoparticles, especially in the case of active Co surface sites emerging in the presence of CO.