First-principle Investigation of the Stability and Vibrational Spectrum of MoSx Nanostructures Grown on Cu(111)

Recent experiments have successfully synthetized MoS$_{\mathrm{X}}$ nanostructures in a controlled manner by evaporating Mo adatoms on the copper sulfide monolayer that forms on Cu(111) upon sulfur preloading [1,2]. STM observations and total-energy calculations based on density functional theory, including van-der-Waals interactions, have proposed several structures for MoS$_{\mathrm{X}}$/Cu(111). In this study, we investigate the plausibility of those structures and provide elements for further experimental substantiation or refutation. In particular, we perform density-functional-theory calculations (including ab intio van-der-Waals interactions) of vibrational spectrum of the proposed structures to (1) attest their dynamical stability; (2) compare their thermodynamic stability as obtained from the total free energy; and (3) provide the vibrational frequencies that uniquely fingerprint the proposed structures. \\[4pt] [1] Kim et al., Langmuir 27, 11650 (2011)\\[0pt] [2] Dezheng D Sun, Angew Chem. Int. Ed. \textbf{51}, 10284-8 (2012)