Description of C(sp²)−C(sp²) Rotation in Butadiene by Density Functionals

The torsional potential of 1,3-butadiene has been calculated using several ab initio methodologies. For each value of the C C−C C torsional angle, the fully relaxed geometry and energy have been determined using the Hartree−Fock (HF) method, Möeller−Plesset perturbation theory up to the second order (MP2), and the coupled-cluster method with single, doubles, and parethentical triples (CCSD(T)), as well as using several exchange-correlation combinations of functionals in density functional theory (DFT) calculations. From the results obtained, the achievements and drawbacks of current density functionals in the description of torsional profiles have been rationalized, and some possible breakthroughs have been proposed to improve their performance.