Peripheral nitrogen topology as a defect-chemical design parameter for electronic and magnetic states in graphene: a first-principles study of pyridinic, pyridazinic, pyrrolic, and pyrazolic configurations

Defect and heteroatom engineering are powerful routes for tuning graphene's electronic and magnetic properties, yet peripheral nitrogen topology around graphene voids remains poorly understood. Using spin-polarized first-principles calculations, we examine four heterocyclic nitrogen configurations, pyridinic, pyridazinic, pyrrolic, and pyrazolic, affecting structure, charge redistribution, electronic states, and magnetism in graphene with a central void. Pyridinic N is energetically most favorable, and nitrogen topology controls local lattice reconstruction, shown by bond-length analysis. Charge-density-difference and Bader analyses show peripheral N atoms act as electron-accumulating centers reshaping the vacancy rim. Pyridinic, pyridazinic, and pyrrolic configurations remain metallic or near metallic, whereas pyrazolic graphene opens a narrow band gap and is spin compensated with zero net magnetization, unlike the finite moments of the other systems. This magnetism traces to N-modulated vacancy-edge states involving N 2p and C 2p orbitals, establishing peripheral nitrogen topology as a metal-free, deterministic defect-chemical switch for spintronic and semiconducting domains.