H and the W(001) Surface Reconstructions: Local Bonding to Surface States

The structural properties of the $\mathrm{W}\mathrm{}\left(001\right)p(1\mathrm{}\times 1)-2\mathrm{H}$ system are predicted by use of all-electron total-energy calculations. Both the vibrational frequency (133 meV) and the work-function change (0.95 eV) are in excellent agreement with experiment at the calculated equilibrium H-W interlayer spacing of 1.12 Å. A proposed electronic driving mechanism, which includes local bonding effects and depends on the character of the ${\overline{\Sigma }}_2$ surface-state wave functions, explains the various observed reconstructions of the clean-W(001) and H/W(001) systems, including symmetries and coverage dependence.