The structure and phase stability of CO adsorbates on Rh(110)

TL;DR

This study uses first-principles calculations to analyze the structure and phase stability of CO adsorbates on Rh(110), revealing the most stable configuration and an order-disorder phase transition at 350 K.

Contribution

The paper provides a detailed first-principles analysis of CO adsorbate structures on Rh(110), including phase transition behavior modeled via an anisotropic 2D Ising model.

Findings

p2mg(2x1) 2CO structure is most stable

CO molecules prefer short-bridge sites with slight tilt

Order-disorder phase transition at 350 K

Abstract

The structure of CO adsorbates on the Rh(110) surface is studied at full coverage using first-principles techniques. The relative energies of different adsorbate geometries are determined by means of accurate structure optimizations. In agreement with experiments, we find that a p2mg(2x1) 2CO structure is the most stable. The CO molecules sit on the short-bridge site (carbon below) with the molecular axis slightly tilted off the surface normal, along the (001) direction. Configurations corresponding to different distributions of tilt angles are mapped onto an anisotropic 2D Ising model whose parameters are extracted from our ab-initio calculations. We find that an order-disorder phase-transition occurs at a temperature T_c=350 K.