Trimethylene isomers and propene: structural and vibrational properties from density functional theory

We present density functional based calculations of the structure and vibrational spectra of cyclopropane, propene and C3H6 diradicals, in singlet and triplet spin configurations. We use the pseudopotential scheme and different approximations for the exchange and correlation functionals, namely local spin density, local spin density plus Becke-Perdew gradient corrections and the gradient-corrected Becke-Lee-Yang-Parr with spin polarization. A critical comparison with first-principles self-consistent field and configuration interaction calculations, when available, as well as with experiment, allows us to establish the good performance of the density functional approaches in describing theme systems and, in particular, the destabilization of the ring structure of cyclopropane.