Water models effective fragment potential

In addition to these external electric or magnetic field as a perturbation parameter, solvents can be another option. Solvents having different dielectric constants would mimic different field strengths. In the recent past, several solvent models have been used to understand the reactivity of chemical species [55,56]. The well-acclaimed review article on solvent effects can be exploited in this regard [57]. Different solvent models such as conductor-like screening model (COSMO), polarizable continuum model (PCM), effective fragment potential (EFP) model with mostly water as a solvent have been used in the above studies. 

In general, for each acid HA, the HA-(H20) -Wm model reaction system (MRS) comprises a HA (H20) core reaction system (CRS), described quantum chemically, embedded in a cluster of Wm classical, polarizable waters of fixed internal structure (effective fragment potentials, EFPs) [27]. The CRS is treated at the Hartree-Fock (HF) level of theory, with the SBK [28] effective core potential basis set complemented by appropriate polarization and diffused functions. The W-waters not only provide solvation at a low computational cost they also prevent the unwanted collapse of the CRS towards structures typical of small gas phase clusters by enforcing natural constraints representative of the H-bonded network of a surface environment. In particular, the structure of the Wm cluster equilibrates to the CRS structure along the whole reaction path, without any constraints on its shape other than those resulting from the fixed internal structure of the W-waters. 

To address the problem of finite system size, the EFP method has also been combined with continuum models in order to model the effects of the neglected bulk solvent [125], The Onsager equation was used to obtain the dipole polarization of the solute molecule (modeled quantum mechanically) and explicit water molecules (modeled by effective fragment potentials) due to the dielectric continuum. Thus the energy becomes... 

Merrill GN, Gordon MS. Study of small water clusters using the effective fragment potential model. J Phys Chem A 1998 102 2650-2657. 

Merrill, G. N., Gordon, M. S. (1998). Study of Small Water Clusters Using the Effective Fragment Potential Model, / Phys. Chem. A, 102, 2650-2657. 

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