Force-field optimization

As discussed in Chapter 2, most force fields are validated based primarily on comparisons to small molecule data and moreover most comparisons involve what might be called static properties, i.e., structural or spectral data for computed fixed conformations. There are a few noteworthy exceptions the OPLS and TraPPE force fields were, at least for molecular solvents, optimized to reproduce bulk solvent properties derived from simulations, e.g., density, boiling point, and dielectric constant. In most instances, however, one is left with the question of whether force fields optimized for small molecules or molecular fragments will perform with acceptable accuracy in large-scale simulations. 

Sun, H., COMPASS An ab initio force-field optimized for condensed-phase applications—Overview with details on alkane and benzene compounds, J. Phys. Chem., 102, 7338, 1998. 

Figure 22, Force-field-optimized structures of the complexes of receptor 14 with triglycine (a), and of receptor 15 with gly-phe-gly. (b). Hydrogen atoms are omitted for clarity. In each case the N-terminus of the peptide is anchored to the crown ether by hydrogen bonding the corresponding C-terminus forms an ion pair with the ammonium group. Additional n-stacking of the side chains is observed in the case of complex (b).

Table 2 Comparison of selected bond lengths and angles from structures determined by X-ray crystallography [81], MM force field optimization, and DFT optimization...

Devereux M, Meuwly M (2010) Force field optimization using dynamics and ensemble-averaged data vibrational spectra and relaxation in bound MbCO. J Chem Inf Model 50 349... 

Hulsmann, M., Muller, T.J., Koddermann, T., Reith, D. Automated force field optimization of small molecules using a gradient-based workflow package. Mol. Sim. 36, 1182-1196 (2011) Koddermann, T., Kirschner, K.N., Vrabec, J., Hulsmann, M., Reith, D. Liquid-liquid equilibria of dipropylene glycol dimethyl ether and water by molecular dynamics. Fluid Phase Eq. 310, 25-31 (2011)... 

Hulsmann, M., Kopp, S., Huber, M., Reith, D. Utilization of efficient gradient and Hessian computations in the force field optimization process of molecular simulations. Comput. Sci. Disc. 6, 015005 (2013)... 

H. Sun,/. Phys. Chem. B, 102,7338 (1998). COMPASS An Ab Initio Force-Field Optimized for Condensed-Phase Applications—Overview with Details on Alkane and Benzene Compounds. 

FIGURE 1.57 Displacement of water molecules by chloroform and DMSO from the silica surface (force field optimized geometry). 

Fyta M, Kalcher I, Dzubiella J, Vrbka L, Netz RR (2010) Ionic force field optimization based on single-ion and ion-pair solvation properties. J Chem Phys 132 024911 Klasczyk B, Knecht V (2010) Kirkwood-Buff derived force field for alkali chlorides in simple point charge water. J Chem Phys 132 024109... 

In this study we have presented the first simulations of solid state NMR spectra of polymers that are based on ab initio quantum chemistry. By combining statistical conformational models, empirical force-field optimization of geometries, and the Individual Gauges for Localized Molecular Orbitals (IGLO) method for the calculation of the chemical shift, it is possible to reproduce the shape and the width of the experimental solid state NMR spectra. 

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