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Two-dimensional (2D) ZrS2 monolayer (ML) has emerged as a promising candidate for thermoelectric (TE) device applications due to its high TE figure of merit, which is mainly contributed by its inherently low lattice thermal conductivity. However, the inadequate understanding of the lattice anharmonicity and its effect on the phonon dispersion and lattice thermal conductivity can be misleading in revealing the actual significance of ZrS2 ML in thermoelectrics. Here we investigated the temperature-dependent phonon dispersions and corresponding thermodynamic parameters along with the lattice thermal conductivity of ZrS2 ML by including the lattice anharmonicity based on the nonperturbative self-consistent phonon (SCP) theory, which was recently implemented and well tested with the experimental results. The higherorder (quartic) force constants were extracted by using an efficient compressive sensing lattice dynamics technique, which estimates the necessary data based on the emerging machine learning program. The phonon frequency of low-energy optical modes is enhanced upon including the quartic anharmonicity. The lattice thermal conductivity is found to be increased (by 21% at 300 K) within the SCP approach, which is due to the relatively low value of phonon linewidth contributed by the anharmonic frequency renormalization. The low energy phonons (below 160 cm -1 ) of ZrS2 ML are found to have major contributions to the lattice thermal conductivity.

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Tin chalcogenides (SnS, SnSe and SnTe) are found to have improved thermoelectric properties upon the reduction of their dimensionality. Here we found the tilted AA + s stacked twodimensional (2D) SnTe bilayer as the most stable phase among several stackings as predicted by the structural optimization and phonon transport properties. The carrier mobility and relaxation time are evaluated using the deformation potential theory -these are found to be relatively high due to the high 2D elastic modulus, low deformation potential constant and moderate effective masses. The SnTe bilayer shows high Seebeck coefficient (> 400 μV/K), high electrical conductivity and ultralow lattice thermal conductivity (< 1.91 Wm -1 K -1 ). High TE figure of merit (ZT) values, as high as 4.61 along zigzag direction, are predicted for SnTe bilayer within the carrier concentration range of the order 10 12 -10 13 cm -2 . These ZT values are much enhanced as compared to the bulk as well as monolayer SnTe and other 2D compounds.

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