Stability and metastability of clusters in a reactive atmosphere: theoretical evidence for unexpected stoichiometries of MgMOx

TL;DR

This study uses a cascade genetic algorithm and ab initio thermodynamics to explore the composition, structure, and magnetic properties of MgMOx clusters, revealing the importance of hybrid DFT functionals for accurate phase diagrams.

Contribution

It introduces a cascade approach combining genetic algorithms and ab initio thermodynamics to accurately predict MgMOx cluster properties and stability.

Findings

Small clusters are in thermodynamic equilibrium when x > M.

Non-stoichiometric clusters show unique magnetic behaviors.

Hybrid DFT functionals are essential for accurate phase diagram predictions.

Abstract

By applying a genetic algorithm in a cascade approach of increasing accuracy, we calculate the composition and structure of MgMOx clusters at realistic temperatures and oxygen pressures. The stable and metastable systems are identified by ab initio atomistic thermodynamics. We find that small clusters (M <= 5) are in thermodynamic equilibrium when x > M. The non-stoichiometric clusters exhibit peculiar magnetic behavior, suggesting the possibility of tuning magnetic properties by changing environmental pressure and temperature conditions. Furthermore, we show that density-functional theory (DFT) with a hybrid exchange-correlation (xc) functional is needed for predicting accurate phase diagrams of metal-oxide clusters. Neither a (sophisticated) force field nor DFT with (semi)local xc functionals are sufficient for even a qualitative prediction.