Evidence of longitudinal resonance and optical subsurface phonons in Al(001)

Abstract

A calculation of the surface phonon dispersion curves of Al(001) based on densityfunctional perturbation theory confirms the intrinsic nature of the controversiallongitudinal surface phonon resonance, which has been reported to occur in mostmetal surfaces. The results support previous density–response pseudopotentialand semi-empirical Born–von-Kàrmàn calculations by Franchini, Bortolani, et al,proving the extended nature of the surface perturbation. The latter implies theexistence of a Lucas pair of optical surface modes localized in the second layer.