RESEARCH ACTIVITIES ON HIGH PERFORMANCE COMPUTING CLUSTERS AT CILEA – 2006 39              ! ""#$%%&’$$ (Received on September 6, 2006)  Le catene lineari di carbonio sono sistemi coniugati particolarmente interessanti dal punto di vista elettronico e vibrazionale per la presenza di interazioni a lungo raggio causate dalla delocalizzazione degli elettroni π. In questo articolo il campo di forze vibrazionale di oligoine idrogenate è studiato mediante calcoli quantomeccanici. In particolare, viene analizzato l'andamento delle interazioni tra le coordinate di stretching dei legami CC rispetto alla distanza tra i legami considerati. I calcoli mettono in luce che il valore di tali costanti decresce lentamente con la distanza. Infine, le conseguenze di questo andamento vengono analizzate in relazione alle curve di dispersione fononiche della catena infinita. Carbon linear chains are interesting π-conjugated systems where long range interactions take place due to the delocalized nature of π electrons. In this contribution the vibrational force field of hydrogen terminated oligoynes of increasing chain lengths is investigated by means of first-principles calculations. In particular it is shown that the interaction force constants between CC stretching coordinates decreases slowly with the distance between the bonds considered. The consequence of such a slow decrease with respect to the phonon dispersion of an infinite chain is discussed. ()* linear carbon chains; first-principles calculations; Raman spectroscopy Introduction Many experiments [1-4] and theoretical studies [5-13] indicate that linear carbon chains are interesting nanostructured systems for their non-linear optical properties and electronic transport properties. Furthermore, their presence has been recently revealed in carbon clusters and carbon nanotubes [14]. Raman spectroscopy is routinely used for studying carbon nanostructured materials. Therefore, a better knowledge of vibrational properties is highly desirable for a better understanding and characterization of this class of materials. In this contribution we investigate the vibrational force field of linear carbon chains of increasing lengths and we assess the influence of commonly used functionals in Density Functional Theory (DFT) on the simulation of Raman spectra.