Reference interaction site models RISM

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],... 

The integral equation method is free of the disadvantages of the continuum model and simulation techniques mentioned in the foregoing, and it gives a microscopic picture of the solvent effect within a reasonable computational time. Since details of the RISM-SCF/ MCSCF method are discussed in the following section we here briefly sketch the reference interaction site model (RISM) theory. 

The original OZ equation can be applied only to liquids composed of spherically symmetrical particles, namely atoms. Chandler and Andersen proposed one of the possible extensions to treat general polyatomic cases, referred to as the reference interaction site model (RISM) or site-site OZ (SSOZ) theory [4], This has been further extended by Hirata and Rossky to be applicable to polar molecules such as water [5], In the RISM theory,... 

Sato presents an alternative method to both continuum solvation models and hybrid QM/MM or ONIOM approaches. This is represented by the reference interaction site model (RISM) formalism when combined to a QM description of the solute to give the RISM-SCF theory. 

Integral equation ideas on the structure of monatomic liquids were first modified and applied to molecular liquids by Chandler and Andersen, Their classic work is now referred to as the reference interaction site model (RISM) of molecular liquids. Polymer RISM (PRISM) is essentially an extension of RISM theory that successfully describes the structure of flexible polymer chains in the liquid state. 

Another, a similar route that considers interactions between individual elements of a system, is the reference interaction site model, RISM. The theory involves computations of the system structure by means of the probability density function, which describes location of all N particles of the system. The binary interactions define the pair-density function ... 

The tetrachloride liquids XCiti (X = C, Si, Ti, V, Ge, Sn etc) make an interesting series for studying aspects of orientational correlation in relation to molecular contours. The various diffraction studies have been surveyed in a paper [253 which uses the reference interaction site model (RISM) to evaluate the partial distribution functions. Data for carbon tetrachloride are particularly instructive as they Illustrate the complementary nature of X-ray and neutron scattering. There are three partial functions gcc( )> weighting factors... 

Among the applications of integral equation theory to solutions, Koga et al. (1996) used a reference interaction-site model (RISM), an approximation due to Chandler and Andersen (1972), to calculate the local solvation behavior of naphthalene in supercritical carbon dioxide. They used a ten-site model for naphthalene and a three-site model for carbon dioxide, in which partial charges were placed on the sites in addition to Lennard-Jones potentials acting between sites on different molecules. Their potential function was a sum over the ten naphthalene sites and the three carbon dioxide sites of terms of the form of Equation 5.11 ... 

The reference interaction site model (RISM) theory of Chandler and Andersen [9, 11, 10] is an extension of the theory of monatomic liquids. In RISM theory, each molecule is envisioned as a collection of spherically symmetric interaction sites. In most applications of RISM theory to small molecule liquids. Chandler and coworkers [9, 11, 12, 13, 10] modeled interaction sites as overlapping hard spheres. The primary difference between RISM theory and monatomic liquid theory is that the correlations can be propagated intramolecularly as well as intermolecularly. Chandler and Andersen generalized the OZ equation as follows for a single component fluid in Fourier space... 

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