  Two-dimensional group IV transition-metal dichalcogenides have encouraging
thermoelectric applications since their electronic and lattice properties can
be manipulated with strain. In this paper, we report the thermoelectric
parameters such as electrical conductivity, Seebeck coefficients, electrical
relaxation times, and the mode dependent contributions to the lattice thermal
conductivity of ZrX$_2$ (X = S, Se, Te) from first principles methods. Our
calculations indicate that due to tensile strain, the powerfactor increases
while simultaneously decreasing the lattice thermal conductivity thus enhancing
the thermoelectric figure of merit. Tensile strain widens the bandgap which
corresponds to higher powerfactor. The lattice thermal conductivity decreases
due to the stiffening of the out-of-plane phonon modes thus reducing the
anharmonic scattering lifetimes and increasing the thermoelectric
figure-of-merit.
