Polarizable point charge

Svishchev IM, Kusalik PG, Wang J, Boyd RJ (1996) Polarizable point-charge model for water results under normal and extreme conditions. J Chem Phys 105(11) 4742 1750... 

Polarizable Point-Charge Model for Water Results Under Normal and Extreme Conditions. 

Coexistence Properties for the Polarizable Point Charge Model of Water and the Effects of Applied Electric Field. 

Numerous polarizable water models have recently been developed [75-82]. At least three types of polarizable models have been used for supercritical water PPC [83], a polarizable TIP-type model [84], and a few variations of SPC-type models with either point or smeared electrostatic charges [78,85,86]. With a few exceptions [87-89] the polarizable models are typically built upon successful non-polarizable counterparts, by scaling the Coulombic charges to match the gas-phase dipole moment, and by including either a polarizable point charge or point dipole to account for the many-body polarization contributions. Moreover, sometimes the permanent dipole moment is set larger than the gas-phase value of 1.85D in order to obtain better agreement with experimental data at ambient conditions [78,82]. 

The polarizable point charge (PPC) model of Kusalik et al [82,83] retains the simplicity of most non-polarizable three-site models while incorporating the nonadditivity polarization through polarizable point charges that fluctuate in response to the local electric field. The novelty in this model is that the electric-field dependence of the point charges has been determined by quantum-chemical calculations using a commercial package. 

Svishchev, I. M. Kusalik, P. G. Wang, J. Boyd, R. J. (1996) Polarizable point-charge Model of Water Results under Normal and Extreme Conditions, Journal of Chemical Physics 105, 4742-4750... 

Niesar-Corongiu-Clementi (NCC) (1990) Polarizable point charge (PPC) (1996) 92 261 R Ab initio Polarizable... 

I. M. Svishchev, P. G. Kusalik, J. Wang, and R. J. Boyd,/. Chem. Phys., 105, 4742 (1996). Polarizable Point-Charge Model for Water Results Under Normal and Extreme Conditions. 

For the sake of illustration and as a way of transition to polarizable point charges, we consider point charges with a dipole moment. The mean potential that an ion of a species i feels involves two parts. 

The SAPT method has recently been used to compute the complete six-dimensional water dimer potential. A global elaborate analytic potential has been fitted to about 1000 points. This potential has been used to compute the second virial coefficient for water. Results are presented in Figure 2. As one can see, the SAPT potential reproduces the experimental data very accurately. Compared to the popular empirical potentials as well as to the MCY ab initio potential the SAPT values are nearly an order of magnitude more accurate. Notice that the virial coefficients computed from the empirical potentials do not include quantum corrections but these are not important at this level of accuracy. The recent polarizable point charge (PPC) potential of Ref. 176, which gives the best virial coefficient of all empirical potentials, has to a lesser extent the effective character typical of bulk empirical potentials as it models explicitly the nonadditive induction energy. Thus, the pairwise additive component is less biased by efforts to mimic nonadditive forces. 

Polarization is usually accounted for by computing the interaction between induced dipoles. The induced dipole is computed by multiplying the atomic polarizability by the electric field present at that nucleus. The electric field used is often only that due to the charges of the other region of the system. In a few calculations, the MM charges have been included in the orbital-based calculation itself as an interaction with point charges. 

More realistic treatment of the electrostatic interactions of the solvent can be made. The dipolar hard-sphere model is a simple representation of the polar nature of the solvent and has been adopted in studies of bulk electrolyte and electrolyte interfaces [35-39], Recently, it was found that this model gives rise to phase behavior that does not exist in experiments [40,41] and that the Stockmeyer potential [41,42] with soft cores should be better to avoid artifacts. Representation of higher-order multipoles are given in several popular models of water, namely, the simple point charge (SPC) model [43] and its extension (SPC/E) [44], the transferable interaction potential (T1PS)[45], and other central force models [46-48], Models have also been proposed to treat the polarizability of water [49],... 

Because this method avoids iterative calculations to attain the SCF condition, the extended Lagrangian method is a more efficient way of calculating the dipoles at every time step. However, polarizable point dipole methods are still more computationally intensive than nonpolarizable simulations. Evaluating the dipole-dipole interactions in Eqs. (9-7) and (9-20) is several times more expensive than evaluating the Coulombic interactions between point charges in Eq. (9-1). In addition, the requirement for a shorter integration timestep as compared to an additive model increases the computational cost. 

Zhu SB, Yao S, Zhu JB, Singh S, Robinson GW (1991) A flexible polarizable simple point-charge water model. J Phys Chem 95(16) 6211—6217... 

Chelli R, Barducci A, Bellucci L, Schettino V, Procacci P (2005) Behavior of polarizable models in presence of strong electric fields. I. Origin of nonlinear effects in water point-charge systems. J Chem Phys 123(19) 194109... 

Banks JL, Kaminski GA, Zhou RH, Mainz DT, Berne BJ, Friesner RA (1999) Parametrizing a polarizable force field from ab initio data. I. The fluemating point charge model. J Chem Phys 110(2) 741—754... 

The evaluation of Gcicctrostatic has received a great deal of attention. It is clear that Eqs. (32) and (33), which are for nonpolarizable point charges and point dipoles, cannot reproduce the effect of the medium upon the solute molecule. A major contribution was made by Onsager, who took this molecule to be a polarizable point dipole located at the center of a spherical cavity 20 the resulting expression is,... 

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