Thermodynamic properties are often modeled by classical force fields which describe the interactions on the atomistic scale. Molecular simulations are used for retrieving thermodynamic data from such models, and many simulation techniques and computer codes are available for that purpose. In the present round robin study, the following fundamental question is addressed: Will different user groups working with different simulation codes obtain coinciding results within the statistical uncertainty of their data? A set of 24 simple simulation tasks is defined and solved by five user groups working with eight molecular simulation codes: DL_POLY, GROMACS, IMC, LAMMPS, ms2, NAMD, Tinker, and TOWHEE. Each task consists of the definition of (1) a pure fluid that is described by a force field and (2) the conditions under which that property is to be determined. The fluids are four simple alkanes: ethane, propane, n-butane, and iso-butane. All force fields consider internal degrees of freedom: OPLS, TraPPE, and a modified OPLS version with bond stretching vibrations. Density and potential energy are determined as a function of temperature and pressure on a grid which is specified such that all states are liquid. The user groups worked independently and reported their results to a central instance. The full set of results was disclosed to all user groups only at the end of the study. During the study, the central instance gave only qualitative feedback. The results reveal the challenges of carrying out molecular simulations. Several iterations were needed to eliminate gross errors. For most simulation tasks, the remaining deviations between the results of the different groups are acceptable from a practical standpoint, but they are often outside of the statistical errors of the individual simulation data. However, there are also cases where the deviations are unacceptable. This study highlights similarities between computer experiments and laboratory experiments, which are both subject not only to statistical error but also to systematic error.
A new version release (4.0) of the molecular simulation tool ms2 (Deublein et al., 2011; is presented. Version 4.0 of ms2 features two additional potential functions to address the repulsive and dispersive interactions in a more versatile way, i.e. the Mie potential and the Tang-Toennies potential. This version further introduces Kirkwood-Buff integrals based on radial distribution functions, which allow the sampling of the thermodynamic factor of mixtures with up to four components, orientational distribution functions to elucidate mutual configurations of neighboring molecules, thermal diffusion coefficients of binary mixtures for heat, mass as well as coupled heat and mass transport, Einstein relations to sample transport properties with an alternative to the Green-Kubo formalism, dielectric constant of non-polarizable fluid models, vapor-liquid equilibria relying on the second virial coefficient and cluster criteria to identify nucleation.
Experimental data on the solubility of carbon dioxide (CO2) in poly(oxymethylene) dimethyl ethers (CH3O(CH2O) n CH3, OME n ) are presented for OME2, OME3, and OME4. The total pressure was measured as a function of the liquid phase composition at 313.15 and 353.15 K for pressures up to 4.3 MPa in a high-pressure view-cell. Henry’s law constants of CO2 in OME2, OME3, and OME4 are determined. They are similar for all studied OME and depend strongly on the temperature. The experimental data are modeled by the original perturbed-chain statistical associating fluid theory equation of state. As a basis, pure component models for OME were developed based on literature data on the liquid density and vapor pressure. The solubility of CO2 in OME is successfully described using a group contribution scheme. The results show that OME are interesting candidates as physical absorbents for CO2.
The activities of the alkali halide salts in aqueous solution are systematically investigated by the molecular simulation of alkali halide salt solutions using a set of ion models developed in previous work by our group in combination with SPC/E water. Five cations and four anions are considered (
A united atom force field for the homologous series of the poly(oxymethylene) dimethyl ethers (OMEn):OMEn are oxygenates and promising new synthetic fuels and solvents. The molecular geometry of the OMEn, the internal degrees of freedom and their electrostatic properties were obtained from quantum mechanical calculations. To model repulsion and dispersion, Lennard-Jones parameters were fitted to the experimental liquid densities and vapour pressures of pure OMEn (n " 1 -4). The critical properties of OMEn (n " 1 -4) were determined from the simulation data. Additionally, the shear viscosity of pure liquid OMEn is evaluated and compared with literature data. Finally, the solubility of CO 2 in OME2, OME3 and OME4 is predicted using a literature model for CO 2 and the Lorentz-Berthelot combining rules. The results agree well with experimental data from the literature.
Der vorliegende Übersichtsartikel berichtet über Fortschritte in der molekularen Modellierung und Simulation mittels massiv‐paralleler Hoch‐ und Höchstleistungsrechner (HPC). Im SkaSim‐Projekt arbeiteten dazu Partner aus der HPC‐Community mit Anwendern aus Wissenschaft und Industrie zusammen. Ziel dabei war es mittels HPC‐Methoden die Vorhersage von thermodynamischen Stoffdaten in Bezug auf Effizienz, Qualität und Zuverlässigkeit weiter zu optimieren. In diesem Zusammenhang wurden verschiedene Themen bearbeitet: Atomistische Simulation der homogenen Gasblasenbildung, Oberflächenspannung klassischer Fluide und ionischer Flüssigkeiten, multikriterielle Optimierung molekularer Modelle, Weiterentwicklung der Simulationscodes ls1 mardyn und ms2, atomistische Simulation von Gastrennprozessen, molekulare Membran‐Strukturgeneratoren, Transportwiderstände und gemischtypenspezifische Bewertung prädiktiver Stoffdatenmodelle.
A united atom force field for the homologous series of the poly(oxymethylene)dimethyl ethers (OMEn): H3C–O–(CH2O)n–CH3, is presented. OMEn are oxygenatesand promising new synthetic fuels and solvents. The molecular geometry of the OMEn,the internal degrees of freedom and their electrostatic properties were obtained fromquantum mechanical calculations. To model repulsion and dispersion, Lennard-Jonesparameters were fitted to the experimental liquid densities and vapour pressures of pureOMEn (n “ 1 - 4). The critical properties of OMEn (n “ 1 - 4) were determined fromthe simulation data. Additionally, the shear viscosity of pure liquid OMEn is evaluatedand compared with literature data. Finally, the solubility of CO2 in OME2, OME3and OME4 is predicted using a literature model for CO2 and the Lorentz-Berthelotcombining rules. The results agree well with experimental data from the literature.
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