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  • Successful modeling of the highly compressed vapor phase of a nitrogen-oxygen mixture at the extreme conditions present in atmospheric lightning strikes and explosions (temperature of 3000 Kelvin and pressure of 30 gigapascal.
    07/25/16

    Researchers develop new approach for studying reaction equilibria in complex chemical systems

Working with a team of national and international collaborators, graduate student Evgenii Fetisov and Professor Ilja Siepmann have developed a new simulation approach to predict reactive equilibria. Those collaborators included researchers at the Argonne National Laboratory, Lawrence Livermore National Laboratory, Massachusetts Institute of Technology, and the Swiss Federal Institute of Technology (ETH) in Zurich.

Understanding reaction equilibria of complex chemical systems is important for chemists and chemical engineers. Because it may be difficult or impossible to conduct experiments at extreme temperatures and pressures (for example, to replicate the conditions in lightning or explosions) or involving hazardous compounds, predictive modeling of reaction equilibria via molecular simulation is especially useful. However, predictive modeling is not a simple task. It is difficult to accurately simulate both strong (short-range) and weak (long-range) interactions and to sample the wide range of time scales present in reactive systems. In addition, many computational approaches require users to specify a set of chemical reactions and ideal gas equilibrium constants—information that may not be known—in advance.

Evgenii Fetisov portrait photo
Evgenii Fetisov

The new simulation approach can be used to predict reaction equilibria without requiring advance specification of chemical reactions and ideal gas equilibrium constants. The researchers' work combines concepts from reactive Monte Carlo and molecular dynamics methods to create a reactive first-principles Monte Carlo (RxFPMC) framework that successfully modeled the highly compressed vapor phase of a nitrogen-oxygen mixture at the extreme conditions present in atmospheric lightning strikes and explosions (temperature of 3000 Kelvin and pressure of 30 giga Pascal). The RxFPMC simulations, using MIRA at the Argonne Leadership Computer facility, yielded valuable insights about the solvation environment and the resulting enhanced concentration of nitrogen oxide in oxygen-rich mixtures. This new method was validated by comparing equilibrium distributions from the RxFPMC approach and from a thermochemical code parameterized to experimental data.

This research was published in ACS Central Science—a flagship American Chemical Society journal, which is entirely open source. Fetisov presented this work at the Midwest Thermodynamics and Statistical Mechanics Conference in May, and Siepmann will present this research at the 2016 American Institute of Chemical Engineers annual meeting, November 13-16, in San Francisco.

This work was supported by the National Science Foundation through Grant CHE-1265849. Part of this work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. This research used resources of the Argonne Leadership Computing Facility, which is a DOE Office of Science User Facility supported under Contract DE-AC02-06CH11357. Additional computer resources were provided by the Minnesota Supercomputing Institute at the University of Minnesota.

First-principles Monte Carlo approach to study reaction equilibria in complex chemical systems
The new first-principles Monte Carlo simulation approach can be used to predict reaction equilibria in complex chemical systems without requiring advance specification of chemical reactions and ideal gas equilibrium constants.