Accurately determining the thermal transport properties of the two-dimensional material ${\mathrm{MoSi}}_2{\mathrm{N}}_4$ is essential for its application in micro- and nanoscale semiconductor devices. To date, substantial discrepancy persists between theoretical prediction and experimental measurement of the thermal conductivity ${\kappa }_L$ of ${\mathrm{MoSi}}_2{\mathrm{N}}_4$, with the underlying physical mechanisms remaining unclear. In this work, the intrinsic ${\kappa }_L$ of ${\mathrm{MoSi}}_2{\mathrm{N}}_4$ is accurately determined by using the neuroevolutionary potential combined with the phonon Boltzmann transport equation (BTE). Taking the temperature-dependent interatomic force constants extracted from effective harmonic model as the inputs, the room-temperature ${\kappa }_L$ of ${\mathrm{MoSi}}_2{\mathrm{N}}_4$ calculated by the BTE method (approximately $351.84\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$) exhibits remarkable consistency with results obtained from a homogeneous nonequilibrium molecular-dynamics method (approximately $343.04\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$). These results underscore the critical influence of higher-order phonon scattering and temperature renormalization of force constants on the intrinsic ${\kappa }_{\iota }$ of ${\mathrm{MoSi}}_2{\mathrm{N}}_4$. Our calculations also demonstrate that the thermal transport performance of ${\mathrm{MoSi}}_2{\mathrm{N}}_4$ could be evidently suppressed by nitrogen vacancy. As for the ${\mathrm{MoSi}}_2{\mathrm{N}}_4$ sample with 0.02% randomly distributed N vacancy, the ${\kappa }_L$ could be decreased to approximately $175\pm 8.96\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$, which provides a plausible explanation for the discrepancy between theoretical predictions and experimental measurements (approximately $173\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$). Interestingly, compared to the internal N vacancy, the surface N vacancy exhibits particularly pronounced effect in suppressing the ${\kappa }_L$ of ${\mathrm{MoSi}}_2{\mathrm{N}}_4$. Such a phenomenon is primarily attributed to significant modifications of the symmetry of the charge density distribution and the geometric environment induced by the surface N vacancy, which weaken Si-N bond interactions and amplify the vibrational motion of Si atoms, thereby enhancing the phonon anharmonicity. This work offers valuable insights into the thermal transport properties of the ${\mathrm{MoSi}}_2{\mathrm{N}}_4$ family and serves as a case study for exemplifying the use of machine-learning interatomic potentials to investigate the impact of low-concentration disordered vacancy defects on the thermal conductivity of materials.

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• Anharmonic lattice dynamics
• Defects
• Lattice thermal conductivity
• Monolayer films
• Boltzmann theory
• Density functional calculations
• Machine learning
• Molecular dynamics