Ab initiostudy of the anomalies in the He-atom-scattering spectra of H/Mo(110) and H/W(110)

Abstract

Helium-atom-scattering (HAS) studies of the H-covered Mo(110) and W(110) surfaces reveal a twofold anomaly in the respective dispersion curves. In order to explain this unusual behavior we performed density-functional theory calculations of the atomic and electronic structure, the vibrational properties, and the spectrum of electron-hole excitations of those surfaces. Our work provides evidence for hydrogen-adsorption induced Fermi-surface nesting. The respective nesting vectors are in excellent agreement with the HAS data and recent angle resolved photoemission experiments of the H-covered alloy system ${\mathrm{Mo}}_{0.95}{\mathrm{Re}}_{0.05}$(110). Also, we investigated the electron-phonon coupling and discovered that the Rayleigh phonon frequency is lowered for those critical wave vectors. Moreover, the smaller indentation in the HAS spectra can be clearly identified as a Kohn anomaly. Based on our results for the susceptibility and the recently improved understanding of the He-scattering mechanism we argue that the larger anomalous dip is due to a direct interaction of the He atoms with electron-hole excitations at the Fermi level.