Molecular modeling, spectroscopic signature and NBO analysis of some building blocks of organic conductors.

Vibrational spectra with IR and Raman intensities in optimum state have been calculated for 2,2'-Bi-1,3-diselenole (commonly known as tetraselenafulvalene) and its halogen derivatives. All these calculations have been done by employing density functional theory (DFT) and second order Moller-Plesset perturbation theory (MP2) methods incorporated with suitable functionals and basis sets. Normal coordinate analysis has also been performed to calculate potential energy distributions (PEDs) to make a conspicuous assignment. The vibrational frequencies of all the four molecules have been assigned using PEDs and the results are compared with available values for the most similar molecules like tetrathiafulvalene. The molecular stability and bond strength have investigated by applying the Natural Bond Orbital (NBO) analysis. The energy gap between HOMO and LUMO is 2.041 eV for tetraselenafulvalene and it is slightly less than 2eV for halogen derivatives which implies that these molecules fall in the wide band gap semiconductor groups.