Geometric structures, vibrational spectroscopic and global reactivity descriptors of nematogens containing strong polar group- A comparative analysis using DFT, HF and MP2 methods

Abstract

The present article deals with the geometric structures and vibrational spectroscopic studies of 4’-n-alkyl-4-cyanobiphenyl (nCB), with propyl (3CB), pentyl (5CB), and heptyl (7CB), strong polar groups that are of commercial and application interest. The computations have been carried out using the Density Functional Becke3-Lee-Yang-Parr (B3LYP) level with the basis set 6-31++G(d.p), Hartree Fock (HF), and second order Moller-Plesset perturbation (MP2) theory with the same basis set. The observed vibrational spectra has been resolved and assigned in detail for comparision with molecules. These results indicate that DFT, HF, and MP2 values are slightly different at three levels. Further, the global reactivity descriptors such as HOMO (E_HOMO), LUMO (E_LUMO), energy gap (E_g), ionization energy (I), electron affinity (A), electro negativity (χ), chemical hardness (η), electronic chemical potential (μ), electrophilicity index (ω), and softness (S) for higher homologous, namely; 7CB has been reported. It has been observed that the substitution of strong polar group with increment in alkyl chain length has profound control on vibrational bands that makes it possible to identify the liquid crystal phases and calculate the orientational order parameters.

Keywords:

• DFT
• HF
• and MP2 methods
• Vibrational spectra
• Nematogens