Force fields transferable

Siepmann, J.I. 2001. Challenges in the development of transferable force fields for phase equilibrium calculations, in Forum 2000 Fluid Properties for New Technologies, Connecting Virtual Design with Physical Reality, Rainwater, J.C., et al., eds. Pp. 110-112. Boulder, CO NIST Special Publication. 

In order to improve MD simulations, a number of specific areas should be addressed in the area of basic molecular dynamics theory. These include (1) development of full quantum mechanical calculations on complex molecules and more robust ways to incorporate quantum mechanical calculations within larger-scale classical mechanics or statistical mechanics approaches (2) development and refinement of transferable force fields between arbitrary atoms and molecules, which are necessary building blocks for MD simulations of general systems and (3) development of multiscale theories and techniques for understanding systems. Moreover, the community must develop toolkits that allow general users to perform such simulations. 

Freeman, D. E., and M. K. Wilson Transferable force fields for chlorinated germanes and silanes. Spectrochim. Acta 21, 1825—1833 (1965). 

What is the system of coordinates that is used to specify and define the molecular energy, and what is the relation of these coordinates to the chemical internal coordinates, i.e., bond lengths, bending angles, and dihedral angles These are not trivial questions and reveal at the outset some of the problems that pertain to the development of unique and transferable force fields. 

The vapour pressure of V2O5 has been determined between 973 and 1473 K, and the enthalpy of evaporation calculated as ca. 143 kJ mol . The electrical conductivity of liquid V2O3 has been measured as a function of both temperature and partial pressure of oxygen. Raman and i.r. spectra or oriented single-crystals of V2O5 have been recorded and the absorption frequencies compared with those calculated using a simple transferred force-field. 2... 

The steering of parallel molecular simulations requires special consideration. This is realized by three different modules the producer, the executer, and the collector. The main function of the producer, illustrated in Fig. 6, is to generate all configuration files for the molecular simulations. In order to generate transferable force fields, a variation level was added to the producer. This allows researchers to vary their optimization jobs by the force-field parameters, number of ensembles, temperatures, and molecular models (i.e., different substances). Before mnning the producer, the user must define all model systems with their properties in the initial configuration file, which contains several sections for each system. The relevant... 

Fang, H.J., Kamakoti, P., Ravikovitch, P.I., Aronson, M., Paur, C., ShoU, D.S. First principles derived, transferable force fields for CO2 adsorption in Na-exchanged cationic zeolites. Phys. Chem. Chem. Phys. 15, 12882-12894 (2013)... 

Garcia-Sanchez, A., Ania, C.O., Parra, J.B., Dubbeldam, D., Vlugt, T.J.H., Krishna, R., Calero, S. Transferable force field for carbon dioxide adsorption in zeolites. J. Phys. Chem. C 113, 8814-8820 (2009)... 

Of course, we are not limited to a quadratic force field we can also include higher order terms, which just require more parameters to model, say, bond stretching more accurately. Thus a simple and transferable force field can look like this ... 

For inorganic systems, it has been more common to specify pairwise interaction parameters individually (see, e.g.. Ref. 86). This is a consequence of the historical emphasis on the simulation of a limited number of compounds within a particular study. However one notable exception is provided by the ionic potential parameters derived by Vessal (see Table 12 in the later section Zeolites and Microporous Materials). In his approach, combining rules were a design constraint in the derivation of the parameter set as a whole. The resulting force field is effective for both the structural and energetic description of a wide range of materials and, in particular, the incorporation of nonframework cations in microporous materials, which can prove an exacting test of more locally derived and less transferable force fields. 

In transferable force fields, the parameters for a given functional group are deemed transferable between different molecules. There are numerous transferable force field families, which were developed for different applications. Below, some families relevant for chemical engineers are described optimized potentials for liquid simulations (OPLS) [96,110-112], transferable potential for phase equilibria (TraPPE) [113-122], optimized potential model for phase equilibria (OPPE) [59, 68, 107, 123-130], Nath, Escobedo, and de Pablo (NERD) force field [100,131-133], and the GIBBS99 exponential-6 force field [18,134], (cf. Table 1). Many force fields families are COTitinuously being improved and extended to include new types of compounds thus numerous versions are available. 

TraPPE and OPPE-UA are, in our opinion, the best transferable force fields developed 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 cOTitributiOTi methods like UNIFAC in phenomenological thermodynamics. 

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 coworkers [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... 

Transferable force fields have the benefit that they are ready to use and do not need to be fitted for each component individually, although at the expense of prediction accuracy. On the other hand, specific force fields, parameterized for a single molecule, are time-intensive in development and require experimental and/or QM data for optimization. Their main advantage is that they can yield excellent accuracies. The advances of the QM methods in recent years allow for the construction of force fields based on high quality ah initio data, i.e., nowadays force fields can be constructed even for new fluids whose properties have been poorly measured or not measured at all. Therefore, molecular modeling and simulation based on classical force fields is a promising alternative route, which in many cases complements the well established methods like classical equations of state or G models. 

Ferrando N, Lachet V, Teuler JM et al (2009) Transferable force field for alcohols and polyalcohols. J Phys Chem B 113 5985-5995... 

The impressive development in molecular simulation stems from important improvement in both codes and computers. It made available accurate atomistic simulation of fluorine derivatives. Depiction of the SPF is most commonly achieved by quantum calculations. The major difficulty in describing interactions involving fluorine atoms actually lies in a correct description of the electrostatic effects [38]. Crystal unit cell dimensions [39,40] and the thermal behavior of fluoropolymers [41 3] were thus originally difficult to reproduce. Dihedral potential energy (Equation 6.3) that plays a central role in the backbone dynamics was also incorrectly depicted. In this section, illustrative examples of force fields specifically dedicated to fluoropolymers and more transferable force fields are reviewed. 

Figure 5.1 Basic specifications of a general, systematic force field for ionic liquids, fa Internal consistency anions and cations are parameterised with the same force field functional, with special attention given to the parameterisation of atomic partial point charges and the flexibility fdihedral angles of the ions. The transfer of parameters from different sources is also checked for adequacy ffor instance, the parameters for the chloride ion are taken from molten salt data, not from aqueous solution results fb Transferability force field parameters are valid within the same homologous family ffor instance, when modelling ions with different alkyl side-chain lengths - bottom double arrow) and allow the possibility of ion interchange to yield different ionic liquids ftop double arrows), (c) Compatibility molecular residues and moieties are taken directly from well-established force fields like OPTS FBI. Simple rules are...

Ad hoc or transferable Force field fitting from ab initio calculations... 

This is convenient for reducing the number of needed parameters. It is also useful for establishing the so-called transferable force field in which a set of parameters are assigned to atom types that can then be used for similar molecules. 

As mentioned, to deal with the considerable gap in number between e q)erimental dipole derivatives and electro-optical parameters, a least squares approach is usually adopted [72], From die available literature it does not become entirely clear how individual parameter values, especially equilibrium bond moments, are derived from the sets of linear equations as defined by Eqs. (3.23) and (3.24). It can be assumed that extended applications to a large number of molecules diat have die same type of structural elements may enable, by multiple testing, to arrive at physically significant electro-optical parameters. In fact, a library of such intraisity parameters has been created and used together with standard transferable force fields to predict die infrared spectra of a number of aliphatic and aromatic hydrocarbons [60-62], Comparisons between calculated and predicted spectra do not, however, appear to be satisfactoiy for many molecules. Thus, the accuracy of both force constants and eop s is under question. On the odier side, the main purpose of these libraries of empirical vibrational parameters... 

While it has to be acknowledged that the calculation of these BVSE landscapes requires a little bit more computational effort than the calculation of bond valence mismatch landscapes, the fact that the same parameters used to calculate these static pathway models are also suitable as a highly transferable force field for molecular dynamics simulations of a wide range of oxides appears to be a major... 

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