Novel electronic properties of monoclinic MP 4 (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 [Formula: see text] (M = Cr, Mo, W) phosphides in monoclinic C2/c ([Formula: see text]) symmetry. Their dynamical stabilities have been confirmed by phonon modes calculations. Detailed analysis of the electronic band structures and density of states reveal that [Formula: see text] is a semiconductor with an indirect band gap of 0.47 eV in association with the p orbital of P atoms, while [Formula: see text] is a Dirac semimetal with an isolated nodal point at the [Formula: see text] point and [Formula: see text] 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 [Formula: see text] to VIIB-[Formula: see text] compounds. These results provide a systematical understandings on the distinct electronic properties of these compounds.