Poly –N = N– linked 1,5-dihydro-1,5-diazocine, the two-dimensional polymer with Dirac insulator properties: ab initio study

Abstract

A new material – the monolayered, π-conjugated, poly dinitrogen-linked 1,5-dihydro-1,5-diazocine – is proposed. Density functional theory calculations reveal that the material is a two-dimensional Dirac insulator with a direct band gap. The generalised gradient approximation (GGA) and the local density approximation (LDA) give band gaps of E gap GGA = 0.045 eV and E gap LDA = 0.035 eV. Anisotropy of the Dirac cones results in variation of Fermi velocities of the charge carriers: [0.85–5.30] × 106 m/s (GGA) and [0.86–5.38] × 106 m/s (LDA). Corresponding effective masses are ∼103 lower than that of a free electron. G0W0 calculations confirm the topology of density functional theory band structure and show band gap of E gap = 0.121 eV. Cohesive energies are estimated at E c GGA = 5.30 eV/atom and E c LDA = 6.15 eV/atom. Thus, the results provide the first evidence for the existence of Dirac insulators among organic polymers.