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 C(3)H(6) 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. Comparison with first-principle self-consistent-field and configuration-interaction calculations, as well as with experiment, allows us to establish the performance of the density-functional approaches.