Because of its exceptional optical and nonlinear properties, ${\mathrm{Li}\mathrm{Nb}\mathrm{O}}_3$ has been widely adopted as a key semiconductor for optical communications, where effective thermal management is vital to ensure device performance and reliability. This study investigates the thermal conductivity of ${\mathrm{Li}\mathrm{Nb}\mathrm{O}}_3$ based on ab initio calculations. By considering the contribution of wavelike phonons and the effect of four-phonon scattering, the calculated thermal conductivity of ${\mathrm{Li}\mathrm{Nb}\mathrm{O}}_3$ at 300 K is $4.54\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$, which matches the experimental value of $4.63\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$. Wavelike mutually coherent phonons contribute significantly to thermal transport, with contributions as high as 25.6% to the total thermal conductivity at 900 K. Four-phonon scattering exhibits a limited but non-negligible impact on thermal conductivity, resulting in a reduction of 4.02%. Spectral analysis reveals that, for particlelike phonons, low-frequency modes from 0 to 6 THz contribute 81.5% to the thermal conductivity. This study clarifies phonon transport mechanisms in ${\mathrm{Li}\mathrm{Nb}\mathrm{O}}_3$, offering valuable guidance for device design.

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• Anharmonic lattice dynamics
• Heat transfer
• Integrated optics
• Lattice thermal conductivity
• Phonons
• Nonlinear optical materials
• Boltzmann theory
• Density functional calculations