DFTB. The DFTB method is an approximation to density-functional theory (DFT). It employs a minimal atomic-orbital valence basis and involves two-center approximations to the Kohn-Sham matrix elements, thus, allowing the Slater-Koster technique for pre-calculation of all integrals, which is the key ingredient to allow a performance boost of about three orders of magnitude with respect to DFT. It is available in three variants, the original DFTB form, DFTB0, does not correct for interatomic charge transfer. The self-consistent charge (SCC) approximation, SCC-DFTB, also known as DFTB2, improves the transferability, in particular to polar systems. It has been later improved to the third-order level (DFTB3). Most widely applied parameters include the mat-sci parameters for DFTB0, the mio parameters for SCC-DFTB, and more recently the 3ob parametrization, applicable to DFTB2 and DFTB3. Spin polarization and spin-orbit coupling (SOC) can also be included. London dispersion interactions are commonly treated using an a posteriori correction or the many-body dispersion (MBD) approach. DFTB2 has been successfully applied to 2D COFs, DFTB3 has not yet been tested carefully with SOC and with periodic boundary conditions. Popular codes covering MOFs and COFs in periodic boundary conditions are dftb+ and AMS/DFTB. The method allows to determine the structure, stacking, electronic, including topological, properties in a first screening approach. An interesting approach to tackle large MOFs and COFs without interlayer conjugation is the Fragmented Molecular Orbitals approach (FMO-DFTB) developed in the Irle group and available in Gamess-US. For more elaborate investigations, DFTB should be substantiated by DFT.