Localization and delocalization of defect states in 2D polyaramid with carbon and nitrogen vacancies

A systematic first-principles investigation of pristine and vacancy-induced 2DPA monolayers is presented to examine how carbon (C) and nitrogen (N) vacancies influence their structural, electronic, and magnetic behavior. The pristine system forms a planar, conjugated framework with a moderate band gap of 2.54 eV and shows non-magnetic semiconducting character. This behavior changes significantly with the introduction of vacancies. The presence of a C-vacancy reduces the band gap to 1.32 eV and introduces localized defect states near the Fermi level, indicating partial electronic localization. A more pronounced effect is observed for the N-vacancy, where the band gap further decreases to 0.43 eV, accompanied by strong electronic delocalization and the onset of quasi-metallic behavior. These modifications in the electronic structure are closely linked to the emergence of magnetism, with both defect systems exhibiting vacancy-induced magnetic states. The nature of charge redistribution follows a similar trend. While the C-vacancy leads to localized charge accumulation around the defect site, the N-vacancy drives charge delocalization across the lattice, reinforcing the observed electronic behavior. Despite these changes, the structural integrity of the system remains intact. The phonon dispersion and ab initio molecular dynamics simulations confirm dynamical and thermal stability, with no structural degradation observed up to 300 K. This stability is further supported by atom-resolved normalized autocorrelation analysis, which shows strong temporal correlations even in the presence of defects. These electronic and structural modifications are also reflected in the surface properties, as the work function increases from 4.59 eV in pristine 2DPA to 5.03 eV and 5.17 eV in C- and N-vacancy systems, respectively, indicating defect-induced charge redistribution and surface dipole modulation.