Optimized potential for liquid simulation OPLS

For the monatomic case ( = = 1), was definedto be a parameter where the latter was taken to be the atomic radius from the Optimized Potentials for Liquid Simulations (OPLS)2°6 force field less 0.09 A, which is an empirical adjustment. In the multicenter case, is defined numerically by a new procedurei that could be thought of as an approximation to the solutions of Equations [6]—[10]. In this procedure, is chosen so that the Gp derived as in a monatomic case is equal to the Gp determined via numerical integration. Thus, one considers M spherical shells i around each atom k and calculates... 

There is a facility of settings where the user can choose different options as per their requirement. The number of site points for a site (15 default) and the number of sites to be found (5 default) should be specified. Three types of grid are available— fine, standard and coarse—defined based on the distance between two points in the grid. Here, standard grid, the default option, is used. One can also choose between a more restrictive and less restrictive option for defining the hydrophobic regions. Two types of force fields are available of which Optimized Potentials for Liquid Simulations (OPLS) 2005 is the default one. In the given example, all default options are used (Fig. 5.3). 

In transferable force fields, the parameters for a given functional group are deemed transferable between different molecules. There are numerous transferable force field families, which were developed for different applications. Below, some families relevant for chemical engineers are described optimized potentials for liquid simulations (OPLS) [96,110-112], transferable potential for phase equilibria (TraPPE) [113-122], optimized potential model for phase equilibria (OPPE) [59, 68, 107, 123-130], Nath, Escobedo, and de Pablo (NERD) force field [100,131-133], and the GIBBS99 exponential-6 force field [18,134], (cf. Table 1). Many force fields families are COTitinuously being improved and extended to include new types of compounds thus numerous versions are available. 

The optimized potentials for liquid simulations (OPLS) force field can be divided into the OPLS-UA (united-atom) [96, 110-112] and the OPLS-AA (all-atom) [57, 67, 92, 103, 135-139] versions. Among the two, the OPLS-UA force field is predominantly used for engineering applications, mainly because it is computatirMi-ally cheaper than the all-atom version. The OPLS-UA force field is available for hydrocarbons [96], amides [110], peptides [110], alcohols [111], or proteins [112]. The OPLS-AA force field was parameterized for small organic molecules and is intended for biochemical applications. The parameters of the OPLS-AA force field are available for a broader range of functional groups and molecules. Thus, besides hydrocarbons [103] and alcohols [57], parameters can be found for thiols [57], sulfides [57], ketones [57], amides [57], amines [139], pyrrole [138], furan [138], diazoles [138], oxazoles [138], proteins [67], and carbohydrates [92], among others. 

Since only a small number of solvents are widely used in organic chemistry and there are only 20 common amino adds in proteins, well-tested empirical potential funaions may be developed and utilized to represent polypeptides and the usual solvents. Indeed, Jorgensen and co-workers have created a series of optimized potentials for liquid simulations (OPLS) for organic solvents and water, and a number of excellent force fields are available for protein simulations.26-30 Thus, it appears to be natural to divide a condensed phase system into quantum mechanical and classical regions according to the priority of interest or of importance. 

In a series of papers dealing with different types of organic families, Jorgensen and his groups have developed the optimized potentials for liquid simulation (OPLS), a force field construction accurately calibrated to reproduce the structure and energetics of organic liquids in Monte Carlo simulations these are reviewed in Section 9.5.2. Another attempt at deriving an empirical force field for molecules in isolation and in condensed phases has been presented by Sun [27]. A compilation of parameters for force field calculations is available [28]. 

Optimized potentials for liquid simulation (OPLS) was designed for modeling bulk liquids. It has also seen significant use in modeling the molecular dynamics of biomolecules. OPLS uses five valence terms, one of which is an electrostatic term, but no cross terms. 

OPES (Optimized Potentials for Liquid Simulations) is based on a force field developed by the research group of Bill Jorgensen now at Yale University and previously at Purdue University. Like AMBER, the OPLS force field is designed for calculations on proteins and nucleic acids. It introduces nonbonded interaction parameters that have been carefully developed from extensive Monte Carlo liquid simulations of small molecules. These nonbonded interactions have been added to the bonding interactions of AMBERto produce anew force field that is expected to be better than AMBER at describing simulations where the solvent is explic-... 

Jorgensen and col. extended their TIPS (Transferable Intermolecular Potentials for Simulations) [120- 122] to several organic liquids. More recently, they developed a new generation of "effective" potentials, which received the denomination of OPLS (Optimized Potentials for Liquid Simulations) [123-127], The standard OPLS philosophy can be summarized in the following three points 1) to keep the form of the potentials simply and easy to evaluate, 2) to include as few new parameters as possible, 3) to produce structural and thermodynamic properties in reasonable accord with experiment. 

OPLS (Optimized Potentials for Liquid Simulations) 46 Optimization 239 Orbital contraction 81 Orbital energy 116 Orbital exponent 77, 157 Orientation polarization 258 Oscillator strength 195 Outer sphere 216 Overlap integral 78, 103, 162 Overlap matrix 103, 143... 

Jorgensen, W. L, and Tirado-Rives, J. The OPLS [optimized potentials for liquid simulations] potential functions for proteins, energy minimizations for crystals of cyclic peptides and crambin./. Am. Chem Soc., 110,1657-1666, doi 10.1021/ja00214a001 [1988]. 

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