One main goal of the US Department of Energy’s (DOE’s) advanced biofuels program is to develop fuels that can be distributed by using the existing infrastructure and to replace existing fuels on a gallon-for-gallon basis. However, producing high-quality biofuels in a sustainable and economically competitive way is technically challenging, especially in a changing global climate. Designing feedstock to efficiently produce biomass and designing new catalysts to efficiently convert biomass-derived intermediates into biofuels are two significant science challenges involved in advanced biofuel development.
The NWChemEx project directly addresses a Priority Goal in DOE’s 2014–2018 Strategic Plan, namely by developing high-performance computational “models demonstrating that biomass can be a viable, sustainable feedstock” for the production of biofuels and other bioproducts. In addition to providing the means to resolve these biofuel challenge problems, NWChemEx will enable exascale computers to be applied toward many molecular-scale challenges, such as developing new materials for solar energy conversion and next-generation batteries, simulating chemical processes in combustion, CO2 capture, H2 production and storage, predicting the transport and sequestration of energy by-products in the environment, and designing new functional materials.
Computational chemistry is a key research technique for developing next-generation technologies. Scientists in the field use precise simulations of atomic and molecular interactions to understand the function of novel compounds and biomolecules, enabling new methods for solar power conversion and energy storage, CO2 capture and transformation into new fuels and materials, and beyond. High performance computing is a critical tool for conducting feasible computational chemistry simulations. Using supercomputers, researchers can create models with sufficient fidelity to simulate physically accurate molecular interactions. However, these simulations require huge computational resources due to the electrochemical and quantum mechanical processes involved in chemical bonding, which causes even modern supercomputers to struggle with models of large atomic systems such as complex catalysts and proteins.
The Exascale Computing Project’s NWChemEx application was created to address this shortcoming, allowing for far larger computational chemistry simulations without sacrificing simulation accuracy or increasing time to completion. Researchers will use these new capabilities to model the transformation of biomass to fuels and other usable products, and to create new technologies and materials to meet U.S. and global sustainability needs.
The extreme complexity of atomic and molecular interactions has greatly limited the scope of legacy computational chemistry simulations. Traditional systems can typically model interactions between hundreds of atoms before being forced to sacrifice accuracy to reduce simulation durations to feasible levels. However, simulations of this size prohibit the direct study of the molecular systems needed to understand and engineer novel materials and biomolecules for new sustainable technologies. To compensate for this deficit, researchers have resorted to using smaller models which approximate complete systems. Unfortunately, these approximations are often inaccurate, and result in incomplete or erroneous results when compared with information gathered from real-world experiments.
NWChemEx has greatly improved the scope of computational chemistry simulations by allowing for the extension of simulations from hundreds of atoms to hundreds of thousands. This huge increase in capacity is enabled by a modular and scalable software set created to run on exascale systems such as Frontier and Aurora, the world’s fastest supercomputers, as well as smaller machines. The NWChemEx team also implemented a new multi-algorithmic approach which allows for extreme accuracy within segments of a simulation—containing thousands of atoms—while modeling less complex or variable parts of a system at lower fidelity. The team has demonstrated these new capabilities through test simulations for the conversion processes of propanol to propene using a zeolite catalyst—a useful transformation for biofuel synthesis—as well as other processes which illustrate protein function.
NWChemEx will enable next-generation supercomputers to be applied toward many molecular-scale challenges with significant benefits to sustainability efforts, such as developing more efficient solar energy conversion and battery technologies, simulating cleaner chemical processes in combustion, enabling feasible hydrogen production and storage, and designing new functional materials. These advances will support economically viable alternatives to fossil fuels in several key areas, including energy generation, manufacturing, and transportation.
The NWChemEx project is redesigning and reimplementing NWChem for pre-exascale and exascale computers. NWChemEx is based on NWChem, an open-source, high-performance parallel computational chemistry code funded by the DOE Biological and Environmental Research (BER) program that provides a broad range of capabilities for modeling molecular systems. NWChemEx will support a broad range of chemistry research important to DOE BER and DOE Basic Energy Sciences on computing systems that range from terascale workstations and petascale servers to exascale computers.
In particular, the NWChemEx project is developing high-performance, scalable implementations of three primary physical models:
To illustrate the performance of NWChemEx on biomolecular systems at the exascale, the ubiquitin molecule was selected as a performance benchmark. Ubiquitin is a protein molecule typical of many biomolecular molecules, and an abundance of experimental data are available from it and its fragments. Although it will be infeasible to run canonical coupled cluster calculations on ubiquitin, which is a 1,231-atom molecule, reduced-scaling CC calculations can be run on it. The availability of both implementations along with a sequence of ubiquitin fragments will allow any inaccuracies in the reduced-scaling method to be identified and corrected.
To illustrate the capability of NWChemEx for chemical reactions, the project will examine several elementary chemical transformations that have been postulated for the conversion of propanol to propene in the H-ZSM-5 zeolite (basic unit cell: Si96O192). Reduced-scaling CC calculations embedded in the water and zeolite environment will be used to redefine the structures and energetics of the postulated elementary steps in the conversion of propanol to propene. Depending on the outcome of these calculations, additional work might be required to characterize the mechanism of this conversion more fully.