TOWARD RELIABLE ADIABATIC CONNECTION MODELS FREE FROM ADJUSTABLE-PARAMETERS

Methods rooted in the adiabatic connection theorem offer a significant improvement over standard density functional approximations. Among th em, the most successful model is the so-called B3LYP functional, which include, three empirical parameters optimized by a best fit to atomiz ation energies, We introduce a related functional, BILYP, in which the ratio between Hartree-Fock and density functional exchange is determi ned a priori from purely theoretical considerations and no further par ameters are present, The numerical results obtained on standard molecu lar data jet and on some 'delicate' chemical systems indicate that thi s model has essentially the same performance as the B3LYP model, but w ithin a more satisfactory theoretical framework. (C) 1997 Elsevier Sci ence B.V.