Assessment of the reliability of the Perdew-Burke-Ernzerhof functionals in the determination of torsional potentials in π-conjugated molecules

We have assessed the reliability of the Perdew-Burke-Ernzerhof (PBE) exchange-correlation functionals for describing conjugation effects in organic materials through analysis of torsional potential profiles. The best agreement with experimental data is obtained for hybrid methods where a fraction of Hartree-Fock exchange is introduced. The performance of the various approaches is discussed by characterizing the contribution to the potential energy curves, of the various terms entering the total energy at the density functional theory level. Analysis of the data points out that much care needs to be taken when using the PBE functionals to investigate processes associated to breaks in conjugation.