Static electronic and vibrational first hyperpolarizability of meta-dinitrobenzene as studied by quantum chemical calculations

In the present study, we report on the results of computations of the electronic and the vibrational contributions to the static first hyperpolarizability (β) of meta-dinitrobenzene molecule. It turned out that the electron correlation effects are much more important for reliable prediction of the electronic counterpart than for determining vibrational corrections: βe value is increased by about 500% passing from the HF to the CCSD(T) level of theory. The preliminary assessment of density functional theory in determination of hyperpolarizabilities shows that harmonic contributions to β, contrary to the purely electronic contributions, are substantially underestimated in comparison with the wave function theory results. Another important finding of this study is that long-range corrected functionals tend to improve upon traditional functionals both in determining electronic as well as vibrational hyperpolarizabilities. It is also demonstrated that the vibrations of the nitro groups have a predominant influence on the vibrational contributions to βvib. The mechanical and electrical anharmonicity correction terms to the vibrational hyperpolarizability were found to be substantially larger than the lowest-order harmonic term.