Jeffrey Errington and Andrew Schultz of SUNY at Buffalo are supported by an award from the Chemical Theory, Models and Computational Methods program in the Division of Chemistry to develop computational methods and tools to predict properties of complex molecular systems. This project is co-funded by the Computational and Data-Enabled Science and Engineering in Chemical, Bioengineering, Environmental and Transport Systems Program in the Division of Engineering. The project focuses on phase (gas, liquid, solid) and interfacial (e.g. where air and water meet) properties. The properties play a key role in many natural phenomena and in numerous industrial processes. Of particular value to scientists and engineers is an understanding of the relationship between the microscopic interactions, for example at the atomic level, and the macroscopic behavior it exhibits. Such information can be used to tune the molecular-level details of a system to obtain a desired behavior. In principle, molecular simulation provides an ideal tool for studying the phase and interfacial behaviors of complex fluids. Although tremendous advancements have been made in this area, there is still a huge need for efficient and effective computational methods. Professors Errington and Schultz and their groups are developing robust new strategies for interrogating the phase and interfacial properties of complex fluids via molecular simulation. Examples that illustrate the need for such methods include the design of separation technologies, energy storage devices, carbon capture strategies, and surface coatings. The results of this research will be implemented in software that is freely available to the broader research community.
The focus of this research is to develop molecular simulation methods that enable one to deduce the bulk and interfacial properties of complex fluids. Two methodological advances are being pursued: (1) a new rigorous strategy for computing the bulk liquid-vapor saturation properties of fluids and (2) a force-based strategy to determine the spreading interface potential within an isothermal-isobaric ensemble. For the first, virial pressure measurements are collected at multiple densities that span the liquid-vapor coexistence region, and subsequently used to construct a volume probability distribution within the isothermal-isobaric ensemble. The method provides the same level of information as commonly-used flat histogram approaches, does not require molecule insertions/deletions, and can be implemented within a molecular dynamics framework. The second methodological advance is aimed at increasing the accessibility of the spreading interface potential method. The interface potential provides important insight regarding qualitative and quantitative aspects of a system's wetting behavior. The general approach provides a means to determine the contact angle of a liquid droplet on a solid substrate in a mother vapor. The project addresses challenges associated with implementing the method within the commonly-used isothermal-isobaric ensemble. The standard approach results in highly elongated simulation boxes that are difficult to work with in practice. The research team has identified a means to significantly reduce the size of the simulation box required via use of a virtual box. The approach leverages force-based strategies to compute the interface potential. When combined with previous developments, this advance provides a rigorous, efficient, and accessible approach for determining the wetting properties of model systems. In a third effort, tools are developed to facilitate coupling of Monte Carlo and molecular dynamics algorithms within a single molecular simulation framework. Such a coupling enhances the efficiency of the methods noted above. Specifically, the group is contributing additional Monte Carlo move types to the publically- and freely-available LAMMPS Molecular Dynamics Simulator. These contributions are expected to be beneficial to the broad LAMMPS user community.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
