Accuracy of theoretical predictions depends on the computational approaches used to describe the basic properties of 2D polymers, including but not limited to the light absorption, band structure, and carrier mobility. The absorption spectrum of 2D polymers can be predicted by computing the imaginary part of the dielectric function according to the Kramer-Kronig relationship. Methods based on the Green's function (G) and screened Coulomb interaction (W, i.e. GW) are most suitable to depict the optical spectrum of periodic crystals of polymers. For example, the optical gap of g-C 3 N 4 was calculated to be 2.6 eV by using GW-BSE method, only 0.1 -0.2 eV smaller than the experimental value . The excitonic band gap of periodic bulk systems can also be estimated by TD-DFT calculations by adapting the Casida equation approach for molecular excitations . Nevertheless, these methods are very expensive and often computationally too expensive for 2D polymers which usually possess dozens of atoms in the unit cell. However, recent progress in the linear scaling of GW theory make such calculations feasible . A viable compromise is offered by hybrid DFT methods (e.g. S06 and PBE0), which are widely used in estimating the electronic and optical properties of 2D polymers and give reliable predictions . For example, Bi et al.