DFT and Monte Carlo study of the W(001) surface reconstruction

The driving force for the W(001) surface reconstruction and electronic structures of pristine and H-covered W(001) surfaces are studied by means of relativistic DFT calculations. The spin-orbit coupling leads to the splitting of the bands. Adsorbed physical monolayer of hydrogen due to forming adsorption bonds stabilizes the (1 x 1) structure of the H/W(001) surface. The performed calculations have not revealed any substantial nesting of Fermi surface, so do not support the Peierls-like charge-densitywave mechanism of the surface reconstruction. The total energy of the (root 2 x root 2)R45 degrees. W(001) surface structure is found to be lower, by 0.14 eV per atom, than for the (1 x 1) W(001). The dependence of the relative intensity of the characteristic LEED reflection on temperature, obtained with the help of Monte Carlo simulations using the interaction energies estimated from DFT calculations, is in good agreement with available experimental data, thus supporting the concept of the order-disorder type of the transition between the low-temperature (root 2x root 2)R45 degrees. and room-temperature (1x1) surface structures of W(001).