Deep multilayer relaxations on the Al(001) surface: Ab-initio all-electron calculations

Abstract

The multilayer relaxations of pure Al001 surface were theoretically analyzed using ab initio all-electron calculations. Big slabs 23 atomic layers+20 vacuum layers were needed to capture the deep pattern of multilayer relaxations. We have obtained an outward relaxation for the surface interlayer distance and deep interlayer relaxations characterized by a damped oscillation wave pattern, with several interlayers by cycle. The first three interlayers were found to be expanded, while the following four interlayers were found to be contracted. A charge density analysis allows us to correlate the outward relaxation with the population imbalance between the atomiclike p and p orbitals of atoms at the surface. Multilayer relaxations are related to the presence of distributed Friedel oscillations in the charge density difference between bulk and bulk-truncated slabs. Work function and surface energy results are also presented and discussed. In order to calculate the latter, a high precision Al bulk energy value was obtained irrespective of whether it is calculated from the fcc symmetry or slab derived when the same method-dependent parameters as well as big slabs are used. Error bars, as a measure of the theoretical precision, are included for all studied properties. Our results agree with the available experimental measurements and, partially, with other theoretical calculations. Previous experimental work on this surface has never considered the possibility of such deep relaxations. Our results should motivate further experimental research on the multilayer relaxations of the Al001 surface.