I am currently studying Siesta (specifically Transiesta) to investigate electronic transport in materials. However, I am confused about the assumptions and applicability of the NEGF method and this software.
Is it necessary for NEGF or Transiesta to assume ballistic transport of electrons? If so, how can I ensure this when building a model? A solid-state physics professor believes that "To use the non-equilibrium Green's function method, both conditions of ballistic transport and no reflection at the contacts must be satisfied" while I read in a doctoral dissertation that "Landauer's formula mainly focuses on ballistic transport, but NEGF has a wider range of applications." Can I assume that NEGF does not require the assumption of ballistic transport when solving the model, and that the assumption is only used when calculating the transmission coefficient and current using Landauer's formula?
Please correct me if I have any misconceptions, as I am not a student majoring in physics. Thank you.