Based on first-principles calculations within the harmonic approximation, the phonon properties and specific heat capacities of 2D honeycomb lattices are investigated. Graphene, germanene, and plumbene manifest interesting phonon properties. The similarities and differences in their nature, for example, the total phonon bandwidth, low-frequency phonon dispersion, and phonon bandgap mostly arise from the significant orbital interactions. These features are reflected in the phonon branch-dependent specific heat capacity. The information obtained in this work about the relative contributions of distinct phonons to different temperature ranges is crucial for energy storage and heat management applications.
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