For example, B3LYP does not have the meta-GGA term, but M06 does. Hybrid and doublehybrid functionals are distinguished by including a percentage of HF exchange, and a percentage of MP2 correlation, respectively. Therefore double hybrid functionals are at least the cost of a MP2 calculation. Range separated functionals (RSF) are another very important development in DFT methods. In RSFs, such as ωB97 family, the percentage of HF exchange depends on the distance between the electrons. This accounts for the electron self-interaction error, and has become incorporated into several of the most modern functionals (i.e. the ones starting with LC or ω). DFT methods with dispersion corrections, which can be either ab initio, or empirical in nature, are notably more accurate than their standard forms as they improve the description of the non-covalent interactions. Grimme's DFT-D3, along with Becke-Johnson (BJ) damping, is one of the most prominent dispersion corrections widely used in the field. On the other hand, wave function based methods (WFT) include Hartree-Fock, post-Hartree-Fock methods viz., Møller-Plesset perturbation theory of different orders (MP2, MP3, MP4), configuration interaction (CI), coupled cluster (CC), and multi-reference methods such as complete active space self-consistent field (CASSCF), in increasing order of complexity in describing electron correlation, and approaching higher accuracy.