Comparison of SCAN+U and r2SCAN+U for Charge Density Wave Instability and Lattice Dynamics in CuTe

Abstract: Identifying an appropriate exchange-correlation functional and computational conditions is essential for explaining the fundamental physics of materials and predicting their properties. Here, we investigate the performance of the meta-GGA functionals SCAN and r2SCAN, with and without a Hubbard U, for describing the charge density wave (CDW) in the quasi-one-dimensional material CuTe. By examining the Te-Te bond modulation, phonon dispersions, and electronic structures, we identify clear differences in how the two functionals capture the structural and dynamical properties of the CDW formation. r2SCAN+U reproduces the experimentally observed Te-chain distortions in the CDW phase and the phonon soft mode at qCDW=(0.4, 0.0, 0.5) in the non-CDW phase, whereas SCAN exhibits unphysical phonon behavior. The atomic displacements of the soft mode agree well with the experimental Te modulation. Despite their similar electronic structures and optimized lattice constants, our results demonstrate that r2SCAN is a more suitable choice than SCAN for describing CDW formation and lattice dynamics in CuTe.