Impact of normal and oblique incidence on the thermoelectric properties of an InSb monolayer: A comparative study

In modeling the transport properties of two-dimensional monolayers, normal incidence (NI) is physically intuitive and computationally economical compared to oblique incidence (OI). However, the impact of the incident direction on thermoelectric (TE) performance remains to be fully understood. In this work, we systematically compare the TE properties of an InSb monolayer under the NI and OI using first-principles calculations combined with the nonequilibrium Green’s function method. We reveal that the OI can quantitatively modify the TE properties. Microscopically, it smooths out the step-like plateaus in the transmission spectra while it no longer enlarges the transmission gaps. Consequently, the electrical conductance, thermal conductance, and figure of merit ZT are highly sensitive to the incident direction, whereas the Seebeck peak-valley pair near the Fermi level remains robust. Furthermore, while the OI suppresses the ZT peak heights, other properties such as the peak number, positions, and overall temperature dependence are conserved. Notably, the discrepancies in ZT induced by different incident directions are inclined to vanish in the low-temperature limit. These findings establish a crucial methodological principle: the NI suffices for qualitatively locating ZT peaks, but quantitative accuracy requires the inclusion of the OI. This work provides essential guidance for selecting appropriate computational schemes in TE simulations of infinite monolayers.