Benchmark study of the linear and nonlinear optical polarizabilities in proto-type NLO molecule of para-nitroaniline

In the present investigation, for the first time, we have performed a thorough study about different functionals and basis sets for linear and nonlinear optical (NLO) properties of paranitroaniline (p-NA), which is considered as proto-type NLO molecule, among organic NLO materials. There is a dire need of such data base for p-NA because many investigators are using such values of p-NA for comparative analysis. A range of different functionals including HF, BLYP, PW91, PBE, B3LYP, M06, M06-2X, PBEO, BHandHLYP, CAM-B3LYP, LC-BLYP, and B3LYP-D3 are applied in conjugation with several commonly basis sets such as 6-31G*, 6-311G*, 6-311G**, 6-311+G**, cc-pVDZ, and cc-pVTZ. A variety of functional and basis sets combinations are calculated and graphically compared with each other. The calculated total dipole moment for the p-NA is found to be 6.79 D which is quite closer to experimentally determined value. The lowest calculated value for linear isotropic polarizability at HF/6-31G* level of theory is 11.74 x 10(-24) esu while higher values observed with remaining all methods especially 14% polarizability increases in presence of basis set with diffuse functions and similar trend of variation is also observed in linear anisotropic polarizability. Similarly, the calculated value of frequency dependent second-order polarizability is found to be 9.59 x 10(-30) esu at PBE0/6-311+G** level of theory which is quite closer to experimental value of 9.6 x 10(-30) esu. A comparison between the calculated and experimental results shows good agreement among geometries, dipole moments and NLO polarizabilities for p-NA. Moreover, the frontier molecular orbital (FMO) and electron density difference map (EDDM) analysis along with density of state (DOS) plots are also presented to get more physical intuitions into the structure-property relationship and electronic communications between terminal accepter and donor groups through 7r-conjugation. The present investigation provides benchmark data including various commonly used functionals and basis sets for the calculation of NLO properties of p-NA. Thus, the present investigation will put straight several future studies when it comes to comparative NLO study of organic materials.