TIP5P water model

Figure 3 Isotherms of the TIP5P water model (shifted by +7. Okhar). Solid line shows the experimental transformation LDA HDA VHDA under isothermal compression. ...

Figure 1 Structural features of the TIP3P, TIP4P and TIP5P water models 2 COMPUTATIONAL METHODS...

The hypothesis is that this extended first-order phase transition line in the (P,T) plane eould end in a critical point which is called the second critical point of water. This critical point has been detected in some of the computer simulations for model water systems. While there exist different values of the critical temperature and pressure with different theoretical models, TIP5P water model (this model provides some properties which are in good agreement with experiments, but discrepancies remain in some others) gives the following values of the critical parameters Tq = 220 K and Pq = 200 MPa. 

T.J. Dick, J.D. Madura, Chapter 5 A Review of the TIP4P, TIP4P-EW, TIP5P, and TIP5P-E Water Models, in Annual Reports in Computational Chemistry, vol 1, ed. by D.C. Spellmeyer (Elsevier, Amsterdam, 2005)... 

Mahoney MW, Jorgensen WL. A five-site model for liquid water and the reproduction of the density anomaly by rigid, nonpolar-izable potential functions. J. Chem. Phys. 2000 112 8910-8922. Rick SW. A reoptimization of the five-site water potential TIP5P for use with Ewald sums. J. Chem. Phys. 2004 120 6085-6093. Horn HW, Swope WC, Pitera JW, Madura JD, Dick TJ, Hura GL, Head-Gordon T. Development of an improved four-site water model for bio-molecular simulations UP4P-Ew. J. Chem. Phys. 2004 120 9665-9678. 

The setup of a simulation system, which includes a protein embedded into a lipid bilayer requires additional efforts in comparison to a system with a soluble protein. There are different choices the researcher has to make regarding to the nature of the phospholipid bilayer used, the temperature at which the simulations should be performed (this also depends on the nature of the bilayer), the force field, the water model (e.g. SPC, SPC/E, TIP3P, TIP4P, TIP5P this also depends on the choice of the force field), and many more. 

TIP4P, TIP5P SPC models, SPC and SPC/E rigid Stillinger and Rahman model, ST2 and the flexible three-centered water model, F3C. " ... 

When simulations are applied to studies on the surfaces and interfaces of ice near T, it is important to select a potential model of H2O that is suitable for simulations of both ice and water near To date, many potential models of H2O have been proposed. Several of the models, such as the extended simple point charge model (SPC/E) [56], T1P4P [57], and TIP5P [58] models, have been used by many researchers, especially for simulations of liquid water. In these models, an H2O molecule is represented as an electrically neutral, simple rigid molecule (Figure 17.11). Commonly in aU of the models, a positive charge is placed on each hydrogen (H) atom. 

In order to understand the differences between the results of the different models, the authors also calculated the interaction energies between water and the ions of the ionic liquid. The results are reproduced in Table 3. The table shows at first that the variation in the interaction energies for the different computational approaches is small. This demonstrates that even small inaccuracies can have significant effects on the output of a simulation. Moreover, the table shows also that the TIP5P model... 

II. Kumar, P., Buldyrev, S. V., and Stanley, H. E. (2007) Water liquid-liquid dynamic crossover and liquid-liquid critical point in the TIP5P model of water, in S. J. Rzoska and V. Mazur (eds.) Soft Matter under Exogenic Impacts , NATO Sci. Series II, vol. 242 (Springer, Berlin)... 

A further analysis of TIP5P by Mahoney and Jorgenson was carried using MD. The calculated diffusion coefficient at 25 °C and 1 atm pressure was found to be 2.62 zb 0.04 X 10 cm s which compares quite well with the experimental value of 2.30 X 10 cm s h The pressure dependence was also in quite good agreement with experiment. The density maximum of water at 4°C was also reproduced quite well by the TIP5P model, as may be seen in Figure 5. The thermodynamic and structural properties of water were determined in terms of the inherent structures or basins of attraction by Starr et alP... 

Using MD simulations [82,83], we studied three models, each of which has a LL critical point. Two (the TIP5P and the ST2) treat water as a multiple-site rigid body that interacts via electrostatic site-site interactions complemented by a Lennard-Jones potential. The third is the spherically symmetric two-scale Jagla potential with attractive and repulsive ramps. In all three models the loci of maxima of the relevant response functions, Ki and Cp, which coincide close to the critical point and give rise to the Widom line, were evaluated. The hypothesis that, for all three potentials, a dynamic crossover occurs when the Widom line is crossed, was carefully explored. 

Finally, the results reported in Fig. 12 have been used to obtain the H2O density and, by using optical methods, to explore the possibility of a minimum in this quantity. Very recently, using neutron scattering, the existence of a density minimum in the supercooled phase has been observed in confined D2O at Tmm = 210 5K [91]. The idea of a minimum located approximately 70K below density maximum temperature Tma has also been suggested by MD simulation studies ]39] in which both the TIP5P-E and the ST2 potential models for water have been used [39,85]. This possibility can also be inferred from simple arguments. After the maximum, the density of bulk water decreases rapidly with decreasing T before T, whereas ice Ih has a smaller density than that of liquid water and, contrary to the behavior of supercooled bulk water, has a normal positive expansivity, that is, p increases... 

The left-hand side of Fig. 25 shows the derivative -Td n8 T)/dT obtained from 8 T) data [133]. Also shown are the Cp T) values measured in bulk water in the interval 244.5K < T < 290K [124] and the same quantity obtained by means of a simulation study from the TIP5P model of water for 210K < T < 290K (right-hand side) [143]. 

Figur 25. The temperature derivative of the measured fractional chemical shift — Td n8 T )/dT (solid circles, left hand side), the specific heat at constant pressure, Cp (right-hand side), measured in bulk water in the supercooled regime (solid line. Ref. [124]), and Cp calculated for the TIP5P model of water (solid squares. Ref. [143]).

Gerig has evaluated force field models for trifluoroethanol-water mixture in order to perform a reliable MD simulation of the system. In this study it was very important to obtain good description of solvent fluorine/solute hydrogen NMR cross-relaxation obtained from solute-solvent nuclear Overhauser effects (NOE). An additional requirement was good agreement between experimental and simulated diffusion coefficients as NMR cross relaxation depends on the diffusion of the components in the mfacture. It was found that OPLS-AA (TFE) and TIP5P-E (H2O) did do a reasonably good work. The mixture will be used as a solvent for small peptides in the future. 

---