RISM integral equation, solute-solvent interactions

The general form of the (RISM) integral equation appropriate for treating solute-solvent interactions which has been derived in the literature is given by " ... 

MC and MD simulations could be replaced by other less expensive methods. We shall quote the use of the integral equation methods called RISM (reference interaction site model) explored by Ten-no et al. RISM methods give solute-solvent site-site correlations functions as MC and MD simulations do. The RISM procedure is inserted into an SCF QM cycle as for combined QM/MM methods based on simulations. We have no direct experience on computational costs of these procedures, but in general RISM calculations are faster by some orders of magnitude than MC simulations. This is paid for by a greater sensitivity of RISM to some features of the integral equation methods, such as the closure expressions one has to use. 

One important class of integral equation theories is based on the reference interaction site model (RISM) proposed by Chandler [77]. These RISM theories have been used to smdy the confonnation of small peptides in liquid water [78-80]. However, the approach is not appropriate for large molecular solutes such as proteins and nucleic acids. Because RISM is based on a reduction to site-site, solute-solvent radially symmetrical distribution functions, there is a loss of infonnation about the tliree-dimensional spatial organization of the solvent density around a macromolecular solute of irregular shape. To circumvent this limitation, extensions of RISM-like theories for tliree-dimensional space (3d-RISM) have been proposed [81,82],... 

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