DFTB3 belongs to the family of tight-binding (TB) methods, which approximate the electronic structure of a system by using limited atomic orbital (AO) basis-set representation. However, unlike conventional TB methods, DFTB3 integrates principles from Density Functional Theory (DFT) through a self-consistent field cycle, allowing a more accurate description of various chemical phenomena. The energy functional encompasses terms of electronic contributions (E H0 , E γ , and E Γ ) and the element specific pairwise RPs (E rep ):