Pseudo jahn-teller origin of buckling distortions in two-dimensional triazine-based graphitic carbon nitride (g-C₃N₄) sheets

Due to its direct band gap and light mass, the recently synthesized triazine-based, graphitic carbon nitride (TGCN) is considered a promising material for future microelectronics. However, despite the structural similarity with completely planar carbon-only graphene, TGCN sheets are different because of the presence of buckling distortions making the TGCN sheets nonplanar. In this article, we show that the sufficiently strong coupling between the unoccupied molecular orbitals (UMOs) with occupied molecular orbitals (OMOs) leads to pseudo Jahn-Teller distortions (PJT) and consequent buckling of TGCN layers. Doping the TGCN with doubly charged cations such as Be²⁺ can suppress the PJT distortions resulting in a completely planar structure. A proper understanding of the mechanism of the PJT effect in TGCN is crucial for tailoring properties that are relevant for practical applications.