Instability, Distortion and Dynamics of the W(100) Surface

A model for the reconstructions of the W(100) surface is presented. Four types of distortions are obtained, along 〈011〉, 〈001〉, 〈100〉 (commensurate), and (× 10) (incommensurate). The 〈011〉 distortion, corresponding to the observed (√2×√2)45° clean surface, is worked out in detail. A distortion magnitude of ∼ 0.35 Å is found, and a surface coherence length ξ≃15° Å close to experiment. The full vibrational spectrum, the distortion penetration, and the anisotropic surface anharmonic energies are also obtained.