On the work function of the surface Mo(0 0 1) and its temperature dependence: an ab initio molecular dynamics study

Ab initio molecular dynamics simulations in NVT ensemble have been performed to investigate the finite temperature structure of the Mo(0 0 1) surface and its effect on work function (ϕ). In accord with previous experimental and theoretical work, our simulations predict that a termination with a stable reconstruction pattern is formed at T  =  123 K. This pattern vanishes when temperature is increased to 423 K or 623 K and a disordered surface phase is formed whose time average corresponds to a bulk-like termination. Our results demonstrate that the surface relaxation is an important factor contributing to thermal variation of ϕ. At the lowest temperature, at which a stable reconstruction pattern is formed, the work function is found to increase by  ∼0.23 eV compared to relaxed unreconstructed surface. The disappearance of stable reconstruction pattern at elevated temperatures leads to a decrease of ϕ by  ∼0.07 eV. In contrast, the values computed for a non-reconstructing surface Mo(1 1 0) at T  =  123 K, 423 K and 623 K are found to be nearly identical to the zero temperature value, which is a consequence of restricted atomic motion due to high packing density in this surface.