Fixed charge force fields

Mobley, D.L., EHimont, ., Chodera, J.D., Dill, K. A. Comparison of charge models for fixed-charge force fields Small-molecule hydration free energies in explicit solvent, J. Phys. Chem. B 2007, 111, 2242-54. 

Mobley DL, Dumont E, Chodera JD (2007) Cmnpaiisrai of charge models for fixed-charge force fields small molecule hydration Iree tmergies in explicit solvent. J Phys Chem B 111 2242-2254... 

Swope WC, Horn HW, Rice JE (2010) Accounting for polarization cost when using fixed charge force fields. II. Method and application for computing effect of polarization cost on free energy of hydration. J Phys Chem B 114 8631-8645... 

D. L. Mobley, E. Dumont, J. D. Chodera, and K. A. Dill, J. Phys. Chem. B, 111(9), 2242—2254 (2007). Comparison of Charge Models for Fixed-Charge Force Fields Small-Molecule Hydration Free Energies in Explicit Solvent. 

A non-equilibrium molecular dynamics procedure is used along with an established fixed charge force field. It is foimd that the simulations quantitatively capture the temperature dependence of the viscosity as well as the drop in viscosity that occurs with increasing water content. Using mixture viscosity models, the authors showed that the relative drop in viscosity with water content is actually less than the predicted values for an ideal system. This means that dissolved water is actually less effective at lowering the viscosity of these mixtures when compared to a solute obeying ideal mixing behaviour. 

Many problems in force field investigations arise from the calculation of Coulomb interactions with fixed charges, thereby neglecting possible mutual polarization. With that obvious drawback in mind, Ulrich Sternberg developed the COSMOS (Computer Simulation of Molecular Structures) force field [30], which extends a classical molecular mechanics force field by serai-empirical charge calculation based on bond polarization theory [31, 32]. This approach has the advantage that the atomic charges depend on the three-dimensional structure of the molecule. Parts of the functional form of COSMOS were taken from the PIMM force field of Lindner et al., which combines self-consistent field theory for r-orbitals ( nr-SCF) with molecular mechanics [33, 34]. 

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