Arguments were presented in favour of an additional softening which those changes of surface force constants that lead to a pronounced “soft” surface phonon mode (e.g. M5) could invoke in the global surface phonon spectrum. This result was illustrated for the W, Mo and Cr (001) surface. Analysis of phonons of an isolated layer was used together with a “perturbation theorem”.

A Comment on the W(001) Surface Stability and Reconstruction. Š.Pick, M.Tomášek: Surface Science, 1983, 130[1], L307-10