Nonlinear Solvation versus Intramolecular Effects

The free energy E( E) invested in creation of a nonequilibrium solvent polarization P can be expressed as a series in even powers of P with the two first terms as follows  

For weak solute-solvent interactions, deviations from zero polarization of the solvent are small, and one can keep only the first, harmonic, term in Eq. [121]. 

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