ST2 water

A. Briinger, C. L. Brooks, III, and M. Karpins. Stochastic boundary conditions for molecular dynamics simulations of ST2 water. Chem. Phys. Lett., 105 495-500, 1982. 

Brunger A, C B Brooks and M Karplus 1984. Stochastic Boundary Conditions for Molecular Dynaniii Simulations of ST2 Water. Chemical Physics Letters 105 495-500. 

A plot of the Lennard-Jones 9-3 form of Equations 7 and 8 for ST2 water interacting with smectite and mica surfaces is shown in Figure 1. Values for the parameters used in Figure 1 are given in Tables II and III, and in reference (23). The water molecule is oriented so that its protons face the surface and its lone pair electrons face away from the surface, and the protons are equidistant from the surface. Note that the depth of the potential well in Figure 1 for interactions with the smectite surface and mica surface are... 

Figure 1. Comparison of ST2 water-surface interactions computed from Equations 7 or 8 using parameters for the Lennard-Jones 9-3 potential in Table II and the delocalized charge magnitude for smectite and mica surfaces in Table III.

Figure 2. (a) Geometrical parameters used in the hydrogen bond deflnition. (b) Quasi-component distribution functions for the parameter R ST2 water at lO C. (From Mezei and Beveridge 1981. )... 

Bruge, Martorana, and Fornili described a Transputer-based concurrent implementation of an MD program for ST2 water molecules. High load balance efficiency was obtained using a task decomposition algorithm that evenly distributed particles and interaction calculations among the processors. 

F. Bruge, V. Martorana, and S. L. Fornih, Mol. Simulation, 1, 309 (1988). Concurrent Molecular Dynamics Simulation of ST2 Water on a Transputer Array. 

Figure 1 Isotherms of the ST2 water model (shifted by +3.2khar) Solid line shows the experimental transformation LDA —> HDA —> VHDA under isothermal...

There are four phases of supercooled ST2 water, which densities at corresponding liquid-liquid coexistence in the temperature interval from about 200 to 235 K are ... 

The obtained distributions of the tetrahedricity measure were used for estimation of the concentration C of the four-coordinated tetrahedrally ordered water molecules. Temperature dependence of this concentration along the liquid-vapour coexistence curve is shown in the upper panel of Fig.5. There is only slight increase of C upon cooling from the liquid-vapour critical temperature to about 350 K (due to the temperature mismatch of ST2 water and real water, about 30 to 35° lower temperature should be expected for real water). The drastic increase of C is evident at lower temperatures, when approaching the liquid-liquid phase transition. At 7 = 270 K, concentrations of the tetrahedrally ordered four-coordinated water molecules in two coexisting phases was found to be about 28% and 46.5%. Such step increase of C is related to a step decrease of density from 0.97 to 0.91 g/cm ... 

To illustrate the solvent effect on the average structure of a protein, we describe results obtained from conventional molecular dynamics simulations with periodic boundary conditions.92,193 This method is well suited for a study of the global features of the structure for which other approaches, such as stochastic boundary simulation methods, would not be appropriate. We consider the bovine pancreatic trypsin inhibitor (BPTI) in solution and in a crystalline environment. A simulation was carried out for a period of 25 ps in the presence of a bath of about 2500 van der Waals particles with a radius and well depth corresponding to that of the oxygen atom in ST2 water.193 The crystal simulation made use of a static crystal environment arising from the surrounding protein molecules in the absence of solvent. These studies, which were the first application of simulation methods to determine the effect of the environment on a protein, used simplified representations of the surround-... 

Figure 45. Time-scale matching for protein-solvent motions. The normalized spectral density for the (a) displacement and (6) the velocity autocorrelation functions of Trp-62 N 1, and (c) for the velocity autocorrelation function of ST2 water. (Note the differences in the timescales.)...

The results of early molecular dynamics simulations depend on the model potential functions and the number of particles used for the computations. Geiger (1981) employed the ST2-water model and 215 water molecules/charged particle. 

Yang Liu, Athanassios Z. Panagiotopoulos, and Pablo G. Debenedetti, Low temperature fluid phase behavior of ST2 water. The Journal of Chemical Physics, 131, 104508 (2009). 

Figure 5. Maxima and minima lines in the supercritical region of the (a) ST2 water and (b) Jagla models.

We thank S. V. Buldyrev and Peter H. Poole for providing original data from computer simulations using the Jagla and ST2 water models, respectively, and for fruitful discussions. Financial support from CUNY, PSC-CUNY-40 award, is acknowledged. 

The thermodynamic behavior of both WAC and BKS silica have been examined in the region of the compressibility miiximum, and in both cases, the pattern of thermodynamic anomalies that occur have been found to be the same, and analogous to those found in simulation studies of water. An example is shown in Figure 2, that compares the equation of state features of ST2 water [7] with WAG silica [9] in the P-T plane. In both cases, a retracing line of density maxima occurs above a monotonic spinodal boundary. The qualitative similarity of these features, despite the widely different T and P scales, is striking, and certainly suggests that a search for an LLPT in these silica models, of the kind found in water simulations, is justified. This is discussed in the next section. 

Figure 2. Equation of state features of (a) ST2 water and (b) WAC silica, projected into the P T plane. Density maxima (dashed lines) and liquid spinodal boundaries (dot-dashed lines) are shown. Isochores of P as a function of T are shown as symbols joined by thin solid lines. Equally spaced isochores are shown from bottom to top in (a) from p = 0.8 to 1.1 g/cm, and in (b) from p = 1.8 to 2.4 g/cm. ...

Boundary Conditions for Molecular Dynamics Simulations of ST2 Water. 

Figure 6 Fraction of water molecules with NN nearest neighbors in the first coordination shell along the liquid-vapor coexistence curve of ST2 water model [10].

The temperature of the wetting transition is sensitive to the used water model and to the pore geometry. The phase diagram of ST2 water in slit-like pore of 24 A width and with Uq = -4.62 kcal/mol is shown in Fig. 25. The temperature of the wetting transition is by about 40° higher than in the case of TIP4P water in cylindrical pore with the same water-surface interaction. In parallel, the critical temperature of the prewetting... 

Brunger A, Brooks CL, Karplus M (1984) Stochastic boundary-conditions for molecular-dynamics simulatirais of St2 water. Chem Phys Lett 105 495-500... 

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