Force Field Parametrization from the Hirshfeld Molecular Electronic Density

The Hirshfeld charges are linearly increased to reproduce the experimental dielectric constant of 10 polar solvents having values between 13 (pyridine) and 182 (N-methylformamide). The OPLS/AA force field is used to obtain the new parameters. The surface tension and liquid density are also target properties to determine the new nonbonding parameters. The charge scaling factor is between 1.2 and 1.3. In addition, properties that were not used in the parametrization procedure, such as the heat of vaporization, self-diffusion coefficient, shear viscosity, isothermal compressibility, and volumetric expansion coefficient are obtained. Binary mixtures of amide/water and amide/amide are also studied. The original parameters of OPLS/AA, CGenFF, and GAFF force fields are evaluated. The TIP4P/ε force field is used to simulate water. The results from this work with the new parameters, for both pure components and binary mixtures, are in better agreement with experimental data than those obtained with the original values for most of the calculated properties. The maximum density of N-methylformamide in aqueous solutions is correctly predicted only with the new parameters. The high value of the dielectric constant of acetamide, formamide, and N-methylformamide is discussed in terms of the chain formation from the hydrogen bond interactions.