MolMod – an open access database of force fields for molecular simulations of fluids

Abstract

The MolMod database is presented, which is openly accessible at http://molmod.boltzmann-zuse.de/ and contains presently intermolecular force fields for over 150 pure fluids. It was developed and is maintained by the Boltzmann-Zuse Society for Computational Molecular Engineering (BZS). The set of molecular models in the MolMod database provides a coherent framework for molecular simulations of fluids. The molecular models in the MolMod database consist of Lennard-Jones interaction sites, point charges, and point dipoles and quadrupoles, which can be equivalently represented by multiple point charges. The force fields can be exported as input files for the simulation programs ms2 and ls1 mardyn, Gromacs, and LAMMPS. To characterise the semantics associated with the numerical database content, a force-field nomenclature is introduced that can also be used in other contexts in materials modelling at the atomistic and mesoscopic levels. The models of the pure substances that are included in the data base were generally optimised such as to yield good representations of experimental data of the vapour-liquid equilibrium with a focus on the vapour pressure and the saturated liquid density. In many cases, the models also yield good predictions of caloric, transport, and interfacial properties of the pure fluids. For all models, references to the original works in which they were developed are provided. The models can be used straightforwardly for predictions of properties of fluid mixtures using established combination rules. Input errors are a major source of errors in simulations. The MolMod database contributes to reducing such errors. KEYWORDS

Thermophysical Properties of the Lennard-Jones Fluid: Database and Data Assessment

“…Despite its simplicity, the Lennard-Jones model fluid yields a realistic representation of simple fluids. 21,22 Due to its importance, it is sometimes even referred to as Lennard-Jonesium [23][24][25] -suggesting that it is viewed as a chemical element. 26 The Lennard-Jones potential is defined as the pairwise additive and spherically symmetric potential…”

Characteristic Curves of the Lennard-Jones Fluid

“…The Lennard-Jones (LJ) potential can be favorably used for testing new theories and simulation methods, e.g., for mixtures, phase changes, non-equilibrium phenomena, and interfaces between phases [8][9][10][11][12][13][14][15][16][17][18][19]. Also, the Lennard-Jones potential is often used as a starting point for the development of many state-of-the-art force fields for complex molecules [20][21][22].…”

Introduction

“…2 taking the example of EngMeta. The specificity of the categories is in ascending order (1)(2)(3)(4), which is also shown in Fig. 1.2.…”

“…a vocabulary (or lexicon). If explanations and definitions are added in a way that is understandable to human readers, this becomes a dictionary; in the field of materials modelling, this includes the molecular model database (MolMod DB) nomenclature [4]. A hierarchy of concepts is a taxonomy, where multiple narrower concepts are subsumed (symbol ) under a broader concept, yielding a tree structure, e.g.…”