Phase-IV and Phase-V*

Two new polymorphs of Niobium Trisulfide (NbS₃), phase-IV and phase-V, have been grown and identified by single crystal x-ray diffraction. The polymorphs have monoclinic structure with space group P2_1/c and P2_1/m, respectively. We have calculated the electronic and vibrational properties of both polymorphs, using ab initio density function theory (DFT) at the PBE and HSE level of theory. Electronic band calculation suggests that phase-IV is a semiconductor with an indirect bandgap of ~0.2 eV (PBE), whereas phase-V is a metal. The phonon energy at the zone-center matches closely with the measured Raman spectra. Moreover, the full phonon dispersion reveals that phase-IV is dynamically stable (no negative phonon branches). On the contrary, phase-V exhibits several negative phonon pockets, specifically along the NbS₃ nanowire growth direction. This is an indicator of a possible charge density wave (CDW) ground state in this polymorph.