Theoretical calculation of the Stark component of the solute-solvent interaction energy.: Validity of the mean field approximation in the study of liquids and solutions

We examine the Stark component of the solute-solvent interaction energy and check the validity of the mean field approximation (MFA) in the theoretical study of liquids and solutions. We considered two types of systems: methanol, ethanol, and propanol liquids and formaldehyde, acetaldehyde, and acetone in aqueous solution. We found that, independent of the level of calculation (HF, MP2, or MCSCF), the errors introduced by MFA are less than 5% in the interaction energy and less than 1% in the dipoles. We propose an approximate expression for the Stark component that reduces the errors in the interaction energy to below 1.6%.