Structural stability, chemical order and reactivity pattern of MopWq clusters, with p + q = 8

Abstract

The electronic structure and related properties of free-standing MopWq atomic clusters, with p + q = 8, are investigated within the framework of the fully unconstrained version of the density functional theory as implemented in the SIESTA code. Starting from the structures of the lowest-energy isomers of pure Mo8 and W8, they are decorated for any possible homotops and their geometries are re-optimized. Binding energies, excess energies and second differences in binding energies are reported and used to discuss relative stabilities of different isomers. Interatomic distances, magnetic moments, average coordination numbers and order parameters are also reported to achieve a better understanding of the structural evolution of the species when Mo atoms are replaced by W atoms and vice versa. Adiabatic ionization potentials, adiabatic electronic affinities and absolute hardnesses are also shown and discussed in the context of the potential reactivity of MopWq clusters against hydrotreatment processes. Those reactivity indexes suggest that the Mo3W5 aggregate should be a good candidate to take part in a reaction governed by a charge transfer process.