Computational thermal transport research is critical to the development of new materials that can address challenging energy and environmental problems. Molecular dynamics (MD) simulations are used extensively to study thermal transport in materials. One of the most widely used MD software packages is the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS). It is the primary aim of this project to create and carefully implement improved thermal transport calculation methods in LAMMPS. This problem is made challenging by the fact that this software has hundreds of thousands of users and the solution must be merged into the core LAMMPS code, as opposed to offered as a modular "plug-in". The three objectives of the project are: (1) to implement a corrected heat flux computation for all supported many-body potentials in LAMMPS, (2) to identify the types of molecular systems most affected by the changed heat flux computations, and (3) educate the LAMMPS community on how to implement heat flux in new potentials correctly as well as train new scientists to contribute professional-quality code to the LAMMPS code base. This research will, among other broad impacts, enable large-scale computational screening of materials to accurately predict their thermal properties, which fulfills one of the key goals of the Materials Genome Initiative (MGI). Furthermore, it is an innovative, scalable, reusable software component that supports training for the broad LAMMPS user community as well as general workforce development via training to undergraduates, and ensures the new software capacities are widely available via the open-source LAMMPS package. Additionally, the project provides professional software engineering training to graduate and undergraduate students via a highly-trained resident software developer and resources from the Center for Research Computing at the University of Pittsburgh. Due to the large user base and open source nature of LAMMPS, the research is expected to have a broad impact; these software innovations will be widely available across both industry and academia.
The most common MD technique to compute thermal conductivity, the Green-Kubo method, yields incorrect results in LAMMPS for the majority of molecular simulations. Although the ramifications of the error in the heat flux for the thousands of papers already published using LAMMPS has yet to be fully determined, preliminary data indicates that for liquid hydrocarbons, the heat flux through a many-body potential can be underreported by 95%, leading to a total error of the heat flux of 22%. Unless correct thermal transport calculations can be achieved and implemented for this widely used and highly optimized software package, research and development of materials with novel thermal properties will be significantly hindered. There is no widely available MD code that is able to correctly compute heat flux. The one exception is for molecular systems where only pair-wise interactions exist (which excludes all molecules with greater than two atoms), in which case the current LAMMPS implementation gives correct results. The heat flux computation problem in LAMMPS was identified more than four years ago, but the lack of a correct implementation in any widely used MD software package speaks to the challenge of finding and dedicating software engineers to do this important work. This project addresses the theory, implementation pathway, and validation strategy for an expansive re-implementation of heat flux computations in LAMMPS for many-body potentials.
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.
