Comparative computational analysis of electronic structure, MEP surface and vibrational assignments of a nematic liquid crystal: 4-n-methyl-4´-cyanobiphenyl Dipendra Sharma ⁎, S.N. Tiwari Department of Physics, D.D.U. Gorakhpur University, Gorakhpur 273009, India abstract article info Article history: Received 19 September 2015 Accepted 17 November 2015 Available online 17 December 2015 The homologues of 4-n-alkyl-4´-cyanobiphenyl liquid crystal series constitute an important class of materials be- cause of their technology development applications. The first member of this series namely, 4-n-methyl-4´- cyanobiphenyl is reported to be a pure nematic liquid crystal. The molecular geometry of this nematogen has been optimized by ab-initio HF/6–31G(d, p) as well as DFT B3LYP/6–31G(d, p) methods using GAMESS pro- gramme. The molecular electrostatic potential surface has been scanned with 0.001 electron/bohr 3 . Molecular and thermodynamic properties such as total energy, dipole moment, entropy, enthalpy, Gibbs free energy, HOMO and LUMO energies have been calculated. Further, vibrational assignments of 4-n-methyl-4´- cyanobiphenyl molecule have been carried out. A computational analysis of results obtained by ab-initio and DFT techniques has been discussed in the light of experimental observations available in literature. © 2015 Elsevier B.V. All rights reserved. Keywords: Liquid crystal GAMESS MEP HOMO LUMO Vibrational assignment 1. Introduction The liquid crystalline state, lying between the crystalline and the iso- tropic liquid states of matter, offers a broad range of applications where its anisotropic but liquid properties can be explained. Although liquid crystalline materials were observed for over a century in 1888 but were recognized as such in 1980's. Presently, liquid crystals have emerged as beautiful, mysterious and soft condensed materials. Due to widespread use in the development of technology, industry and bio- medical applications, scientists from almost all the disciplines have fo- cused their attention on liquid crystal science [1–5]. Certain type of molecules form LC phases when heated above their melting points. However they all are anisotropic and differ either in their shape or solubility properties. Derived from the shape of constitut- ing molecules, LCs are differentiated into three main categories: calamatic, discotic and banana shaped liquid crystals. The most com- mon type of molecules of LCs are rod shaped molecules (i.e. one molec- ular axis is larger than the other two axes) forming calamatic liquid crystal. Calamatic liquid crystals may be considered as the classical liq- uid crystals. Because of their elongated shape, under appropriate condi- tions, molecules exhibit orientational and/or positional order; accordingly they are categorized as nematic, smectic etc. [6–8]. The mo- lecular structure of a typical rod-like liquid crystal molecule consists of two or more benzene rings connected by a central linkage group and alkyl or alkoxy chain at the terminals. It is the nature and strength of var- ious types of molecular interactions operating between sides, planes and ends of a pair of molecules, which are solely responsible for the liquid crystalline behaviour of molecules [6]. In view of the key role of molecu- lar interactions in mesogenic compounds, semi-empirical and quantum mechanical studies have been reported [9–16]. Further, availability of high speed computers have facilitated the understanding of liquid crys- tallinity based upon the computer simulation, modelling and quantum chemical techniques [17–27]. The maps of molecular electrostatic potential (MEP) are being systematically used in scientific research for over fifty years [28]. Advances in the graphic and computational devices have increased the use of MEP surfaces, HOMO and LUMO as tools for studying molecular reactivity, charge transfer, interactions and other molecular properties [29–33]. However, to correlate the molecular struc- ture with liquid crystalline properties at the molecular level still remains an elusive goal. In view of the above facts, molecular structure, molecular electro- static potential surface, HOMO and LUMO studies and vibrational as- signments of 4-n-methyl-4′-cyanobiphenyl (1CB) molecule have been carried out using ab-initio HF/6–31G(d,p) and DFT B3LYP/6–31G(d,p) techniques with GAMESS programme [34,35]. 2. Method of calculation The molecular structure of 4-n- methyl-4´-cyanobiphenyl (1CB) molecule has been optimized by both ab-initio (RHF) and density Journal of Molecular Liquids 214 (2016) 128–135 ⁎ Corresponding author. E-mail addresses: d_11sharma@rediffmail.com (D. Sharma), sntiwari123@rediffmail.com (S.N. Tiwari). http://dx.doi.org/10.1016/j.molliq.2015.11.045 0167-7322/© 2015 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Journal of Molecular Liquids journal homepage: www.elsevier.com/locate/molliq