Thermodynamic Properties for Applications in Chemical Industry via Classical Force Fields - Multiscale Molecular Methods in Applied Chemistry - page 223

continuously developed, improved, and refined. Therefore, numerous versions of
each family can be found in the literature.
4.1.7 Force Fields Comparison
Martin [ 169 ] compared the AMBER, CHARMM, COMPASS, GROMOS, OPLS-
AA, and TraPPE force fields with respect to their ability to predict vapor-liquid
equilibrium properties and the liquid density of small alkanes and alcohols. He
concluded that the force field families performing best for fluid phase simulations
are TraPPE and CHARMM. CHARMM better predicts the vapor density, while
TraPPE has a higher accuracy for liquid density predictions.
TraPPE and OPPE-UA are, in our opinion, the best transferable force fields devel-
oped to date for chemical engineering applications. However, they still have some
deficiencies. The capabilities of these force field families are still less explored than
group contribution methods like UNIFAC in phenomenological thermodynamics.
4.2 Specific Force Fields
A force field that is carefully parameterized for a specific substance is usually more
accurate than a transferable force field. Therefore, when high levels of accuracy are
required, specific force fields are preferred. Most of the newer specific force fields
developed for engineering applications were parameterized to reproduce experimen-
tal data on saturated liquid density and enthalpy of vaporization. The use of ab initio
calculations gained importance in the last decade and the majority of force field
developers nowadays thus makes use of QM calculations to some extent. There are
numerous parameterization strategies for the development of such force fields, which
depend on the availability of experimental data and the complexity of the chosen
functional form. There is an immense number of specific force fields; therefore it is
impossible to give a comprehensive overview here. Only a small selection will be
discussed in the following to exemplify different parameterization strategies. The re-
parameterization of existing or transferable force fields using a different set of
experimental or ab initio data as in [ 170 ] will not be treated in further detail.
4.2.1 Empirical Force Fields
All transferable force fields discussed in Sect. 4.1 employ point charges to account
for the molecular charge distribution, although a more accurate description of the
electrostatics with higher multipole moments may be used. Hasse, Vrabec, and co-
workers [ 102 , 109 ] proposed a set of simple united-atom force fields for more than 70
compounds of different classes that describe the intermolecular interactions using
two LJ 12-6 sites plus a point dipole (15) or a point quadrupole (16). The potential