A simple descriptor and predictor for the stable structures of two-dimensional surface alloys

TL;DR

This paper introduces a simple, computationally efficient descriptor, the effective coordination number, for predicting the stability of two-dimensional surface alloys, correlating well with enthalpy of mixing and offering an alternative to complex methods.

Contribution

The authors propose an easily computed descriptor, $ ext{E}$, that predicts alloy stability and correlates with DFT results, simplifying surface alloy analysis.

Findings

$ ext{E}$ correlates with enthalpy of mixing from DFT calculations.

The most stable structures have the highest or lowest $ ext{E}$ depending on magnetic properties.

Replacing $ ext{E}$ with $ ext{E}^*$ retains accuracy and avoids DFT calculations.

Abstract

Predicting the ground state of alloy systems is challenging due to the large number of possible configurations. We identify an easily computed descriptor for the stability of binary surface alloys, the effective coordination number $\mathscr{E}$. We show that $\mathscr{E}(M)$ correlates well with the enthalpy of mixing, from density functional theory (DFT) calculations on $M_x$Au$_{1-x}$/Ru [$M$ = Mn or Fe]. At each $x$, the most favored structure has the highest [lowest] value of $\mathscr{E}(M)$ if the system is non-magnetic [ferromagnetic]. Importantly, little accuracy is lost upon replacing $\mathscr{E}(M)$ by $\mathscr{E}^*(M)$, which can be quickly computed without performing a DFT calculation, possibly offering a simple alternative to the frequently used cluster expansion method.