Sigma enlarging bridge correction of three dimensional Ornstein–Zernike theory for solvation free energy of polyatomic solutes immersed in Lennard-Jones monatomic solvent

We have studied the applicability of the sigma enlarging bridge (SEB) correction method to the solvation of polyatomic solute molecules in a Lennard-Jones monatomic solvent using the three dimensional Ornstein–Zernike (3D-OZ) theory. It is found that the SEB correction improves the solvation free energy (SFE) significantly. It has been concluded from the analysis of the radial distribution function (RDF) that the parameter included in the SEB function can be transferred from the values of the monatomic solute to those of the polyatomic one for the 3D-OZ theory. The one dimensional reference interaction site model (1D-RISM) theory has also been examined. The SEB correction is found to be applicable to improve the SFE of the 1D-RISM theory. Except for buried or sterically hindered atoms of the solute, the transferability of the SEB parameter has been confirmed in terms of the RDF obtained by the 1D-RISM theory. This paper also examines the applicability of the hybrid closure between the molecular dynamics simulation and the one of the following closure equations—the hyper-netted chain, Kovalenko–Hirata, or Kobryn–Gusarov–Kovalenko equation—for preparing the solvent–solvent correlation function. Using the results of the hybrid closure in addition to the SEB-corrected closure, we discuss the effect of the quality of the correlation functions for the bulk solvent on the accuracy of the SFE.