Electronic structure calculation of bulk and monolayer MoS 2 has been performed using plane wave pseudopotential method based on density functional theory. The indirect band gap in the bulk MoS 2 was found to be 0.9 eV, whereas in the monolayer-MoS 2 the band gap of 1.57 eV was found to be direct one. The calculated physical parameters of monolayer MoS 2 are found to be very close to the bulk MoS 2 and compare well with available experimental and other theoretical results. The calculated density of states (DOS) may help explain this change in the nature of band gap in bulk and in monolayer MoS 2 . A further variation in band gap has been observed in MoS 2 monolayer on applying biaxial strain.
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.
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