  Topological insulators (TI) are materials having an energy band gap in the
bulk and conducting helical electronic states on the surface. The helical
states are protected by time reversal symmetry thus are expected to be robust
against static disorder scattering. In this work we report atomistic first
principles analysis of disorder scattering in two-probe transport junctions
made of three dimensional TI material Bi2Se3. The robustness of the device
against disorder scattering is determined quantitatively. Examining many
different scattering configurations, a general trend emerges on how strong the
perturbing potential and how it is spatially distributed that can derail the
helical states on the Bi2Se3 surfaces.
