  LaAgSb$_{2}$ is a Dirac semimetal showing charge density wave (CDW) order.
Previous ARPES results suggest the existence of the Dirac-cone-like structure
in the vicinity of the Fermi level along the $\Gamma$-M direction [X. Shi et
al., Phys. Rev. B 93, 081105(R) (2016)]. This paper is devoted to a complex
analysis of the electronic band structure of LaAgSb$_{2}$ by means of
angle-resolved photoemission spectroscopy (ARPES) and theoretical calculations
within the direct ab initio method as well as tight binding model formulation.
To investigate the possible surface states we performed the direct DFT slab
calculation and the surface Green function calculation for the (001) surface.
The appearance of the surface states, which depends strongly on surface, points
to the conclusion that LaSb termination is realized in the cleaved crystals.
Moreover, the surface states predicted by our calculations at the $\Gamma$ and
$X$ points are found by ARPES. Nodal lines, which exist along X--R and M-A path
due to crystal symmetry, are also observed experimentally. The calculations
reveal another nodal lines, which originate from vanishing of spin-orbit
coupling and are located at X-M-A-R plane at the Brillouin zone boundary. In
addition, we analyze band structure along the $\Gamma$-M path to verify,
whether Dirac surface states can be expected. Their appearance in this region
is not confirmed.
