Physically founded phonon dispersions of few-layer materials and the case of borophene

<p>By building physically sound interatomic force constants, we offer evidence of the universal presence of a quadratic phonon branch in all unstrained 2D materials, thus contradicting much of the existing literature. Through a reformulation of the interatomic force constants (IFCs) in terms of internal coordinates, we find that a delicate balance between the IFCs is responsible for this quadraticity. We use this approach to predict the thermal conductivity of Pmmn borophene, which is comparable to that of , and displays a remarkable in-plane anisotropy. These qualities may enable the efficient heat management of borophene devices in potential nanoelectronic applications.</p> <p><b>IMPACT STATEMENT</b> The newly found universality of quadratic dispersion will change the way 2D-material phonons are calculated. Predicted results for borophene shall become a fundamental reference for future research on this material.</p>