  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.
This work investigates the effect of the lattice anharmonicity driven by
temperature-dependent phonon dispersions on thermal transport of ZrS2 ML. The
calculations are based on the self-consistent phonon (SCP) theory to calculate
the thermodynamic parameters along with the lattice thermal conductivity. The
higher- order (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 as an alternative of
computationally expensive density functional theory calculations. Resolve of
the degeneracy and hardening of the vibrational frequencies of low-energy
optical modes were predicted upon including the quartic anharmonicity. As
compared to the conventional Boltzmann transport equation (BTE) approach, the
lattice thermal conductivity of the optimized ZrS2 ML unit cell within SCP +
BTE approach is found to be significantly enhanced (e.g., by 21% at 300 K).
This enhancement is due to the relatively lower value of phonon linewidth
contributed by the anharmonic frequency renormalization included in the SCP
theory. Mainly, the conventional BTE approach neglects the temperature
dependence of the phonon frequencies due to the consideration of harmonic
lattice dynamics and treats the normal process of three-phonon scattering
incorrectly due to the use of quasi-particle lifetimes. These limitations are
addressed in this work within the SCP + BTE approach, which signifies the
validity and accuracy of this approach.
