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In computational chemistry, classical water models are used for the simulation of water clusters, liquid water, and aqueous solutions with explicit solvent. The models are determined from quantum mechanics, molecular mechanics, experimental results, and these combinations. To imitate a specific nature of molecules, many types of model have been developed. In general, these can be classified by following three points; (i) the number of interaction points called ''site'', (ii) whether the model is rigid or flexible, (iii) whether the model includes polarization effects. An alternative to the explicit water models is to use an implicit solvation model, also known as a continuum model, an example of which would be the COSMO Solvation Model or the Polarizable continuum model (PCM) or a hybrid solvation model. ==Simple water models== The rigid models are known as the simplest water models which rely on non-bonded interactions. In these models, bonding interactions are implicitly treated by holonomic constraints. The electrostatic interaction is modeled using Coulomb's law and the dispersion and repulsion forces using the Lennard-Jones potential. The potential for models such as TIP3P and TIP4P is represented by where ''kC'', the electrostatic constant, has a value of 332.1 Å·kcal/mol in the units commonly used in molecular modeling; ''qi'' are the partial charges relative to the charge of the electron; ''rij'' is the distance between two atoms or charged sites; and ''A'' and ''B'' are the Lennard-Jones parameters. The charged sites may be on the atoms or on dummy sites (such as lone pairs). In most water models, the Lennard-Jones term applies only to the interaction between the oxygen atoms. The figure below shows the general shape of the 3- to 6-site water models. The exact geometric parameters (the OH distance and the HOH angle) vary depending on the model. : 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Water model」の詳細全文を読む スポンサード リンク
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