  The effect of impurities on a superconductor with Bogoliubov Fermi surfaces
(BFSs) is studied using a realistic tight-binding model. Based on the band
structure composed of $d$-orbitals in tetragonal FeSe, whose S-doped sample is
a potential material for BFS, we construct the superconducting state by
introducing a time-reversal broken pair potential in terms of the band index.
We further consider the effect of impurities on the BFS, where the impurity
potential is defined as a local potential for the original $d$-orbitals. The
self-energy is calculated using the (self-consistent) Born approximation, which
shows an enhancement of the single-particle spectral weight on the Fermi
surface. This is consistent with the previous phenomenological theory and is
justified by the present more detailed calculation based on the FeSe-based
material.
