The main objective of the project is the development, improvement and testing of the methodology for evaluation of the nonlinear optical (NLO) properties with focusing on effects of electron correlation and effects of the vibrational motion of nuclei. Suitability of selected long-range corrected density functional (LC-DFT) methods for the evaluation of NLO responses will be tested and relevant parameters will be optimized to improve their accuracy and reliability in hyperpolarizability calculations. The methods will be tested primarily on chemically interesting p-conjugated oligomeric systems characterized by an asymmetric unit cell with anticipated large second-order NLO responses. Particularly, we plan to include various derivates of oligoacetylene chains, H–[HC=CR]n–H, with R=F and Cl.