  MXenes are a family two-dimensional transition metal carbide and nitride
materials, which often exhibit very good metallic conductivity and are thus of
great interest for applications in, e.g., flexible electronics,
electrocatalysis, and electromagnetic interference shielding. However,
surprisingly little is known about the fermiology of MXenes, i.e, the shape and
size of their Fermi-surfaces, and its effect on the material properties. One
reason for this may be that MXene surfaces are almost always covered by a
mixture of functional groups, and studying Fermi-surfaces of disordered systems
is cumbersome. Here, we study fermiology of four common Ti-based MXenes as a
function of the surface functional group composition. We first calculate the
effective band structures of systems with explicit mixed surfaces and observe
gradual evolution in the filling of the Ti-d band and resulting shift of
Fermi-level. We then demonstrate that these band structures can be closely
approximated by using pseudohydrogenated surfaces, and also compare favorably
to the experimental angle-resolved photoemission spectroscopy results. By
modifying the pseudohydrogen charge we then proceed to plot Fermi-surfaces for
all systems and extract their properties, such as the Fermi-surface area and
average Fermi-velocity. These are in turn used to evaluate the electrical
conductivity with the relaxation time fitted to experimentally measured
conductivities.
