Abstract

The linear (alpha), and nonlinear (beta, gamma) optical NLO properties of ortho-, meta- and para-nitrophenol (ONP, MNP and PNP) isomers have been calculated in gas phase by using ab initio (HF, MP2 and MP4) and density functional theory (DFT) (B3LYP, CAM-B3LYP) methods, with the 6-31+G(d,p) and 6-311+G(3d,3p) standard and the Sadlej specialized basis sets. These properties were evaluated both at static and at dynamic regime within the finite field FF numerical techniques and the time-dependent-Hartree-Fock approach at 1,910 nm, respectively. Additional calculations were performed for the beta static hyperpolarizability of these isomers in presence of p-dioxane solvent with the Onsager Model and the SCRF-PCM approach, using B3LYP/6-31+G(d,p) and MP2/6-31+G(d,p) levels of theory. Additionally, CCSD/6-31+G(d,p) calculations were performed for the alpha, beta and gamma properties of PNP isomer. The B3LYP and MP2 alpha (ave) results of the nitrophenol isomers are comparable to the experimental alpha (ave) reports; while the tendency for the beta (v) calculated values (beta (v) PNP > beta (v) MNP > beta (v) ONP), that can be explained in terms of the O (x) atomic charge of the -NO2 group, does not follow exactly the experimental ones. The B3LYP gamma (ave) results are in correspondence to the experimental measurements, the correlation of which is r (2) = 0.99. The use of FF methodology in conjunction with the B3LYP and MP2 methods and the 6-31+G(d,p) basis set show to be appropriate approaches to predict qualitative optical properties of Push-Pull like organic molecules, provided are considered the solvent effects or frequency dependence. However, to have a clear picture of the NLO properties of an isolated molecule, higher order correlation effects combined with specialized basis sets, frequency and solvent effects should be employed. We have demonstrated that MP4/Sadlej level of theory is able to reproduce NLO properties that can be considered equivalent to those from more sophisticated approaches, such as CCSD together with extended basis sets.