Electronic transport in titanium carbide MXenes from first principles

We compute from first principles the electronic, vibrational, and transport properties of four known MXenes: ${\mathrm{Ti}}_{3}{\mathrm{C}}_{2}, {\mathrm{Ti}}_{3}{\mathrm{C}}_{2}{\mathrm{F}}_{2}, {\mathrm{Ti}}_{3}{\mathrm{C}}_{2}{(\mathrm{OH})}_{2}$, and ${\mathrm{Ti}}_{2}{\mathrm{CF}}_{2}$. We study the effect of different surface terminations and monosheet thickness on the electrical conductivity, and show that the changes in conductivity can be explained by the squared velocity density of the electronic state, as well as their phonon scattering lifetime. We also compare the solution of the iterative Boltzmann transport equation (IBTE) to different linearized solutions, namely, the self-energy relaxation time approximation (SERTA) and the momentum relaxation time approximation (MRTA), and we show that the SERTA significantly underestimates the electrical conductivity while the MRTA yields results in better agreement with the IBTE. The computed monolayer conductivity at 300 K is in reasonable agreement with reported experimental measurements.