Phonons in Copper Diphosphide (CuP₂): Raman Spectroscopy and Lattice Dynamics Calculations

Copper diphosphide (CuP2) is an emerging binarysemiconductorwith promising properties for energy conversion and storage applications.While functionality and possible applications of CuP2 havebeen studied, there is a curious gap in the investigation of its vibrationalproperties. In this work, we provide a reference Raman spectrum ofCuP(2), with a complete analysis of all Raman active modesfrom both experimental and theoretical perspectives. Raman measurementshave been performed on polycrystalline CuP2 thin filmswith close to stoichiometric composition. Detailed deconvolution ofthe Raman spectrum with Lorentzian curves has allowed identificationof all theoretically predicted Raman active modes (9A(g) and9B(g)), including their positions and symmetry assignment.Furthermore, calculations of the phonon density of states (PDOS),as well as the phonon dispersions, provide a microscopic understandingof the experimentally observed phonon lines, in addition to the assignmentto the specific lattice eigenmodes. We further provide the theoreticallypredicted positions of the infrared (IR) active modes, along withthe simulated IR spectrum from density functional theory (DFT). Overallgood agreement is found between the experimental and DFT-calculatedRaman spectra of CuP2, providing a reference platform forfuture investigations on this material.