The famous B3LYP hybrid functional

 

The B3LYP approach belongs to the hybrid approximations for the exchange–correlation functional. The approximation is famous, because it gives very good results and, therefore, is extremely popular. So far so good, but there is a danger of Babylon type science.³¹ It smells like a witch's brew for the B3LYP exchange–correlation potential E_xc: take the exchange–correlation energy from the LSDA method, add a pinch (20%) of the difference between the Hartree–Fock exchange energy³² $E_{\text{x}}^{KS}$ and the LSDA $E_{\text{x}}^{\text{LSDA}}$. Then, mix well 72% of Becke exchange potential $E_{\text{x}}^{\text{B88}}$ which includes the 1988 correction, then strew in 81% of the Lee–Yang–Parr correlation potential $E_c^{\text{LYP}}$. You will like this homeopathic magic potion most (a “hybrid”) if you conclude by putting in 19% of the Vosko–Wilk–Nusair potential³³:

(11.40)$E_{\text{xc}}=E_{\text{xc}}^{\text{LSDA}}+0\cdot 20\left(E_{\text{x}}^{\text{HF}}-E_{\text{x}}^{\text{LSDA}}\right)+0\cdot 72E_{\text{x}}^{B88}+0\cdot 81E_{\text{c}}^{\text{LYP}}+0\cdot 19E_{\text{c}}^{\text{VWN}}\cdot$

If you do it this way − satisfaction is (almost) guaranteed, your results will agree very well with experiment.