First-principles study of TiB2(0001) surfaces

The TiB2(0001) surfaces are calculated using the first-principles total-energy plane-wave pseudopotential method based on density functional theory. It is found that there are large relaxations within the top three layers for both termination surfaces, and the outermost and second interlayer relaxations for B-terminated surfaces are much larger than those for Ti-terminated surfaces. The charge depletion in the vacuum and the charge accumulations in the interlayer region between the first and second layers reinforces the interlayer Ti-B chemical bonds and reduces the outermost interlayer distance. Simultaneously, the charge accumulation for B-terminated surface is more than that for Ti-terminated surface, and the interlayer Ti-B bonds between the second and third layers are weakened more for the B-terminated surface. The Ti-terminated surface is thermodynamically more favourable in most of the range of slab B.