Surface energies, work functions, and surface relaxations of low index metallic surfaces from first-principles

TL;DR

This study uses first-principles calculations to analyze the surface energies, work functions, and relaxations of various low-index metallic surfaces, highlighting convergence issues and discrepancies with experimental data.

Contribution

It provides a detailed comparison of computational methodologies for surface properties and discusses the limitations of current density-functional approximations.

Findings

Calculated surface energies and work functions often do not match experimental values.

Convergence of surface properties depends strongly on slab thickness and computational setup.

Local and semi-local functionals have limitations in accurately predicting surface properties.

Abstract

We study the relaxations, surface energies, and work functions of low index metallic surfaces using pseudopotential plane-wave density-functional calculations within the generalized gradient approximation. We study here the (100), (110), and (111) surfaces of Al, Pd, Pt, and Au and the (0001) surface of Ti, chosen for their use as contact or lead materials in nanoscale devices. We consider clean, mostly non-reconstructed surfaces in the slab-supercell approximation. Particular attention is paid to the convergence of these quantities with respect to slab thickness; furthermore, different methodologies for the calculation of work functions and surfaces energies are compared. We find that the use of bulk references for calculations of surface energies and work functions can be detrimental to convergence unless numerical grids are closely matched, especially when surface relaxations are being considered. Our results and comparison show that calculated values often do not quantitatively match experimental values. This may be understandable for the surface relaxations and surface energies, where experimental values can have large error, but even for the work functions, neither local nor semi-local functionals emerge as an accurate choice for every case.