Assessment of a new local exchange functional OPTX

We evaluate the performance of a new local exchange functional OPTX [N.C. Handy and A.J. Cohen, Mol. Phys. 99 (2001) 403] in predicting thermochemistry and molecular structures. OPTX was developed taking into account that exchange and left–right correlation are non-separable. Used with the correlation functional LYP, OLYP (=OPTX+LYP) significantly improves upon the well-established BLYP. This is attributed to the accurate description by OPTX of the Kohn–Sham exchange (KSX) energy, parameterised against atomic exchange energies. The superiority of OPTX is most evident based on molecular energetic predictions at stretched geometries, where hybrid functionals severely deteriorate. OLYP is recommended in place of BLYP for computational chemistry.