  We introduce a fully ab initio theory for inelastic scattering of any atom
from any surface exciting single phonons, and apply the theory to helium
scattering from Nb(100). The key aspect making our approach general is a direct
first-principles evaluation of the scattering atom-electron vertex. By
correcting misleading results from current state-of-the-art theories, this
fully ab initio approach will be critical in guiding and interpreting
experiments that adopt next-generation, non-destructive atomic beam scattering.
