Transferable Potentials for Phase Equilibria–United Atom Description of Five- and Six-Membered Cyclic Alkanes and Ethers

Abstract

While the transferable potentials for phase equilibria-united atom (TraPPE-UA) force field has generally been successful at providing parameters that are highly transferable between different molecules, the polarity and polarizability of a given functional group can be significantly perturbed in small cyclic structures, which limits the transferability of parameters obtained for linear molecules. This has motivated us to develop a version of the TraPPE-UA force field specifically for five- and six-membered cyclic alkanes and ethers. The Lennard-Jones parameters for the methylene group obtained from cyclic alkanes are transferred to the ethers for each ring size, and those for the oxygen atom are common to all compounds for a given ring size. However, the partial charges are molecule specific and parametrized using liquid-phase dielectric constants. This model yields accurate saturated liquid densities and vapor pressures, critical temperatures and densities, normal boiling points, heat capacities, and isothermal compressibilities for the following molecules: cyclopentane, tetrahydrofuran, 1,3-dioxolane, cyclohexane, oxane, 1,4-dioxane, 1,3-dioxane, and 1,3,5-trioxane. The azeotropic behavior and separation factor for the binary mixtures of 1,3-dioxolane/cyclohexane and ethanol/1,4-dioxane are qualitively reproduced.

On interfacial properties of tetrahydrofuran: Atomistic and coarse-grained models from molecular dynamics simulation

“…We also consider the original TraPPE model of Keasler et al 28 In this model, as usual in TraPPE force fields, the bond lengths between di↵erent chemical groups are fixed. Monomeric units separated by two bonds interact through a harmonic bending potential with the usual form, with bending force constants taken from the TraPPE-UA force field for n-alkanes and ethers.…”

“…Finally, Keasler et al 28 developed a new version of the TraPPE-UA force field (Transferable Parameters for Phase Equilibria-United Atoms) specifically for five-and six-membered cyclic alkanes and ethers, including THF. In particular, they took into account that partial charges are molecule specific and thus they were parametrized using liquid-phase dielectric constants.…”

Predicting hydrophobic solvation by molecular simulation: 2. New united‐atom model for alkanes, alkenes, and alkynes

“…The previous paper of this series [17] compared the performance of three popular UA alkane models, OPLS-UA [8], GROMOS [10] and TraPPE [11][12][13][14], for predicting hydrophobic solvation, i.e., solvation free energies of alkane solutes in alkane solvents. It was found that all three force-fields showed systematic deviations from experimental data [18,19], with OPLS-UA and GROMOS overestimating the magnitude of solvation (by 15% and 13%, respectively), and TraPPE slightly underestimating it (by 6%) [17].…”

“…However, they tend to perform worse than their all-atom counterparts in predictions of dynamic properties (e.g., diffusion and viscosity) [15] because the coarse-graining of the interaction sites leads to less accurate dynamics. Moreover, the complete neglect of electrostatics and polarization means that they are unable to predict dielectric properties, although all-atom fixed-charge models do not appear to perform much better in this respect [16].The previous paper of this series [17] compared the performance of three popular UA alkane models, OPLS-UA [8], GROMOS [10] and TraPPE [11][12][13][14], for predicting hydrophobic solvation, i.e., solvation free energies of alkane solutes in alkane solvents. It was found that all three force-fields showed systematic deviations from experimental data [18,19], with OPLS-UA and GROMOS overestimating the magnitude of solvation (by 15% and 13%, respectively), and TraPPE slightly underestimating it (by 6%) [17].…”

“…As explained previously, the starting point for the improved model is the TraPPE force-field. Bonded parameters were kept the same as in the original TraPPE model, as they lead to a satisfactory description of alkane conformations in the liquid state [11][12][13][14] and their impact on solvation free energies is likely to be minor. For the alkynes, the bonded parameters from OPLS-AA [33] were used (Table S1), as these were not available in TraPPE.…”