We investigate heat transport through a central harmonic chain coupled at its ends to two identical harmonic leads, which serve as heat reservoirs, within the nonequilibrium Green's function formalism. The central chain and the leads are characterized by different masses and spring constants, while the interfacial coupling $\tau$ is treated as an independent parameter. For a homogeneous central chain, we derive an integral expression for the thermal conductance $G$, which explicitly reveals its size-independent behavior in the thermodynamic limit. In this limit, the integral can be evaluated analytically in several cases: the classical limit with strong interfacial coupling, the classical limit with $\tau$ equal to the bond strength in the leads, and the weak interfacial coupling regime. Numerical simulations demonstrate that the theory developed for the thermodynamic limit remains accurate even for finite chains with as few as 100 atoms. The approach is further extended to estimate the size dependence of $G$ in chains with correlated mass disorder and weak, correlated bond disorder. These results show that the system-size scaling behavior of $G$ is insensitive to mass-spring correlations, impedance mismatch between the central chain and the leads, and interfacial coupling.

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• Nonequilibrium statistical mechanics