Flexible water models

Ferguson D M 1995. Parameterisation and Evaluation of a Flexible Water Model. Journal of Computational Chemistry 16 501-511. 

One of the first applications of CMD to a realistic and important system was to study the quantum dynamical effects in water. It was found that, even at 300 K, the quantum effects are remarkably large. This finding, in turn, led us to have to reparameterize the flexible water model (called the SPC/F2 model) in order to obtain good agreement with a variety of experimental properties for the neat liquid. An example of the large quantum effects in water can be seen in Fig. 3 in which the mean-spared displacement correlation function, ( x(t) - x(0) 2) is plotted. (These are new results which are better converged than those in Ref 34.) Shown are the quantum CMD and the classical MD results for the SPC/F2 model. The mean-squared displacement for the quantized version of the model is 4.0 X 10- m s-f while the classical value is 4.0 x 10 m s-f The error in these numbers is about 15%. These results suggest that quantum effects increase the diffusivity of liquid water by a factor of two. 

Multistate Empirical Valence Bond Approach to a Polarizable and Flexible Water Model. 

G. Toth, Ab initio pair potential parameter set for the interaction of a rigid and a flexible water model and the complete series of the halides and alkali cations, J. Chem. Phys. 105, 5518-5524 (1996). 

In the presence of strong intermolecular forces, as they occur in hydrogen bonded liquids, the assumption of undeformable molecules is fairly restrictive. Flexible water models have been developed in order to describe the response of intramolecular geometries to intermolecular forces. Among others, the BJH model [38] has been used frequently in a variety of studies of electrochemical system by Heinzinger and coworkers and other groups. 

Driesner T, Cummings PT (1999) Molecular simulation of the temperature- and density-dependence of ionic hydration in aqueous SrCl2 solutions using rigid and flexible water models. J Chem Phys 111 5141-5149... 

Liquid water is an important medium in which most biomolecules perform their function. Pure liquid water may seem like a very simple system, where one may be able to identify the determining factors of its properties easily, but this is not always found to be the case. Table 2 gives examples of studying several thermodynamic properties of liquid water using a flexible SPC water model in a molecular dynamics simulation. This flexible water model was characterized by the following interaction potential ... 

Wallqvist, A. Teleman, O. (1991) Properties of Flexible Water Models, Molecular Physics... 

The rotational relaxation of water molecules is often discussed in terms of angular momentum autocorrelation functions (e g., Stillinger and Rahman 1972 Yoshii et al. 1998). For a flexible water model, a slightly different approach can also be used. In order to separate the various modes of molecular librations (hindered rotations) and intramolecular vibrations, the scheme proposed by Bopp (1986) and Spohr et al. (1988) can be employed. The instantaneous velocities of the two hydrogen atoms of every water molecule in the molecular center-of-mass system are projected onto the instantaneous unit vectors i) in the direction of the corresponding OH bond (ui and U2) ... 

Trokhymchuk AD, Holovko MF, Heinzinger K (1993) Static dielectric properties of a flexible water model. 

Wallqvist A, Teleman O (1991) Properties of flexible water models. Mol Phys 74 515-533 Walrrfen GE (1973) Raman spectra from partially deuterated water and ice-VI to 10.1 kbar at 28°C. JSol Chem 2 159-171... 

The ENCAD (energy calculations and dynamics) force field has been developed by Levitt et al. for the molecular dynamics simulations of proteins and nucleic acids in solution. It employs all-atom force field parameters. For condensed phase simulations the new three-center, flexible water model has been developed. The stress has been laid on the energy conservation effect during molecular dynamics simulations without coupling simulated systems to the thermal bath. The following expression has been used to calculate potential energy of the molecular systems ... 

Vibrational spectroscopy has proven especially important in the experimental characterization of water clusters [18-23]. Unfortunately, even the newer flexible (i.e. non-rigid monomer) water models do not fare well at accoimting in a quantitative manner for the frequency shifts of the OH stretch vibrations of extended H-b ending networks. The problem here is well understood and stems from the limitation of generating flexible water models by simply grafting the force fleld of the monomer onto a rigid monomer model potential... 

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