Novel electronic properties of monoclinic MP4 (M = Cr, Mo, W) compounds with or without topological nodal line

Transition metal phosphides hold novel metallic, semimetallic, and semiconducting behaviors. Here we report by ab initio calculations a systematical study on the structural and electronic properties of MP 4 (M = Cr, Mo, W) phosphides in monoclinic C 2/ c ( C 2 h 6 ) symmetry. Their dynamical stabilities have been confirmed by phonon modes calculations. Detailed analysis of the electronic band structures and density of states reveal that CrP 4 is a semiconductor with an indirect band gap of 0.47 eV in association with the p orbital of P atoms, while MoP 4 is a Dirac semimetal with an isolated nodal point at the Γ point and WP 4 is a topological nodal line semimetal with a closed nodal ring inside the first Brillouin zone relative to the d orbital of Mo and W atoms, respectively. Comparison of the phosphides with group VB, VIB and VIIB transition metals shows a trend of change from metallic to semiconducting behavior from VB-MP 4 to VIIB- MP 4 compounds. These results provide a systematical understandings on the distinct electronic properties of these compounds.