Calculation of the Free Energy of Polarization: Quantifying the Effect of Explicitly Treating Electronic Polarization on the Transferability of Force-Field Parameters
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- 作者：Daan P. Geerke ; Wilfred F. van Gunsteren
- 刊名：Journal of Physical Chemistry B
- 出版年：2007
- 出版时间：June 14, 2007
- 年：2007
- 卷：111
- 期：23
- 页码：6425 - 6436
- 全文大小：370K
- 年卷期：v.111,no.23(June 14, 2007)
- ISSN：1520-5207
文摘
The lack of an explicit description of electronic polarization in nonpolarizable force fields usually results inan incomplete transferability of force-field parameter sets when applied in simulations of the system of interestin either a polar or an apolar environment. For example, the use of nonpolarizable parameter sets optimizedto reproduce experimental data on properties of pure liquids of polar compounds commonly yields too lowsolubilities in water for the corresponding compounds. The reason is that the fixed charge distributions calibratedfor the pure liquid might correspond to too low molecular dipole moments in case of hydration. In the currentstudy, we quantitatively show that explicit inclusion of electronic polarization can improve the transferabilityof biomolecular force-field parameter sets. With this aim, free energies of polarization, 
Gpola, have beencalculated, with Gpola corresponding to the free energy difference between identical systems described by apolarizable and a nonpolarizable model. Using a nonpolarizable model and a polarizable one (based on thecharge-on-spring approach) for dimethyl ether (DME), which were both parametrized to reproduce experimentalvalues for pure liquid properties, small values were found for Gpola for the pure liquid or when a DMEsolute was solvated in the apolar solvent cyclohexane. For the solute hydrated in water, however, Gpola wasfound to be of the same order of magnitude as the discrepancy between the free energy of hydration fromsimulation using a nonpolarizable solute model and the experimental value. Thus, introducing polarizabilitiesclearly improves the transferability of the parameter set. Additionally, in calculations of an anion solvated inDME, Gpola for the solvent adopted relatively large values. From an estimation of the errors in the calculatedfree energy differences, it was furthermore shown that the calculation of Gpola offers an effective and accuratemethod to obtain differences in solvation (or excess) free energies between systems described by polarizableand nonpolarizable models when compared to a direct calculation of solvation (or excess) free energies.
Gpola, have beencalculated, with Gpola corresponding to the free energy difference between identical systems described by apolarizable and a nonpolarizable model. Using a nonpolarizable model and a polarizable one (based on thecharge-on-spring approach) for dimethyl ether (DME), which were both parametrized to reproduce experimentalvalues for pure liquid properties, small values were found for Gpola for the pure liquid or when a DMEsolute was solvated in the apolar solvent cyclohexane. For the solute hydrated in water, however, Gpola wasfound to be of the same order of magnitude as the discrepancy between the free energy of hydration fromsimulation using a nonpolarizable solute model and the experimental value. Thus, introducing polarizabilitiesclearly improves the transferability of the parameter set. Additionally, in calculations of an anion solvated inDME, Gpola for the solvent adopted relatively large values. From an estimation of the errors in the calculatedfree energy differences, it was furthermore shown that the calculation of Gpola offers an effective and accuratemethod to obtain differences in solvation (or excess) free energies between systems described by polarizableand nonpolarizable models when compared to a direct calculation of solvation (or excess) free energies.