Do symbols represent the real world at atomic scale?

Computer simulations are highly promising to accelerate the molecular engineering of green energy technologies, such as new systems for the storage of electric energy and the use of solar energy, as well as the capture of carbon dioxide from the environment. However, the predictive power of these symbols depends on having a way to prove that they are in fact a description of the real world.

This is not a simple test. Many assumptions go into the setting of these symbols. As a result, the samples must be carefully analyzed using an appropriate “verification protocol” that includes an experimental measurement.

“We focused on a solid / melt interface because materials have a ubiquitous interface, and those between oxygen and water are critical in many energy applications.” – Giulia Galli, co-founder theorist at Argonne and the University of Chicago

To address this challenge, a team of scientists at the Argonne National Laboratory at the U.S. Department of Energy (DOE), the University of Chicago and the University of California, Davis, developed a modern diagnostic protocol for simulations of the atomic structure of the interface between solid (a metal oxide) and melt water. The team was led by Giulia Galli, a co-located theorist at Argonne and the University of Chicago, and Paul Fenter, an Argonne tester.

“We focused on a solid / melt interface because materials have a ubiquitous interface, and those between oxygen and water are essential in many energy applications,” Galli said.

“To date, most validation protocols have been designed for large products, bypassing interfaces,” Fenter said. “We felt that the structure at the atomic level of surface and interface in real-world environments would reflect a very sensitive and challenging test method.”

The design method they designed uses high-resolution X-ray (XR) reflection measurements as the experimental column of the protocol. The team compared XR measurements for an aluminum oxide / water interface, fabricated at the 33-ID-D beamline at the Argonne Advanced Photon Source (APS), with results obtained by running high-performance computer simulations at Argonne Leadership Computing Facility (ALCF). Both the APS and ALCF are DOE Science Office User Resources.

“These measurements detect the reflection of high-energy X-ray conduits from an oxide / water interface,” said Zhan Zhang, a physicist in Argonne’s X-ray Science department. At the beam energies generated at the APS, the X-ray waves resemble interregional distances. This allows the researchers to directly study the molecular scale structure of the interface.

“This makes XR a real probe to get experimental results that compare exactly to simulations,” said Katherine Harmon, a graduate student at Northwestern University, a visiting student of Argonne and the paper’s first author. simulations at the ALCF using the code Qbox, which is designed to study the finished temperature properties of materials and molecules using symbols based on quantum mechanics.

“We were able to validate several estimates of the theory,” said Francois Gygi of the University of California, Davis, part of the team and lead developer of the Qbox code. The team compared measured XR intensities with those measured from a number of symbolic structures. They also examined how scattering X-rays from the electrons in different parts of the sample would inhibit the extraction of the test-confirmed signal.

The team’s effort turned out to be more challenging than expected. “Admittedly, it was a bit of a trial and error at first when we were trying to understand the right geometry for acceptance and the right theory that would give us the right results,” said Maria Chan, co. -author of the study and scientist at Argonne Center for Nanoscale Materials, DOE Office of Science User Resource. “However, our back and forth paid off between theory and experiment, and we were able to establish a robust validation protocol that is now possible can also be used for other interface resources. “

“The validation protocol helped to measure the strengths and weaknesses of the simulations, paving the way for more accurate models of hard / melt interface building in the future,” said Kendra Letchworth-Weaver. An assistant professor at James Madison University, she developed software to predict XR signals from simulations during a postdoctoral fellowship at Argonne.

The symbols also take a fresh look at the XR measurements themselves. In particular, they showed that the data are sensitive not only to the atomic conditions, but also to the electron dispersion around each atom in subtle and complex ways. These insights will be useful for future experiments on the oxygen / liquid interface.

The interdisciplinary team is part of the Midwest Integrated Center for Computing Materials, headquartered at Argonne, a DOE-supported computing materials science center. The work is presented in an article entitled “Determining the computational molecular dynamics calculations of an oxygen / water interface with X-ray reflection data,” which appeared in the November 2020 issue of Corporate Review Materials. This project was supported by the DOE Office of Basic Energy Sciences, a Laboratory-led Research and Development Award, and the Department of Defense. ALCF computing time was provided through the ASCR DOE Leadership Computing Challenge.

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About the Argonne Center for Nanoscale Materials

The Center for Nanoscale Materials is one of the five DOE Nanoscale Science Research Centers, a leading national consumer resource for interdisciplinary research at the nanoscale with support from the DOE Science Office. Together, the NSRCs comprise a suite of support facilities that provide researchers with state-of-the-art capabilities to manufacture, process, identify and model nanoscale materials, and the Enterprise’s largest infrastructure investment. National nanotechnology. The NSRCs are available at DOE’s National Laboratories Argonne, Brookhaven, Lawrence Berkeley, Oak Ridge, Sandia and Los Alamos. For more information on the DOE NSRCs, visit https: //science.osti.gov /User Resources /User-Resources-on-eye.

Argonne Leadership Computing Facility providing supercomputing capabilities to the scientific and engineering community to advance basic discovery and understanding in a wide range of subjects. Supported by the U.S. Department of Energy’s (DOE) Office of Science, Advanced Scientific Research (ASCR) program, the ALCF is one of two DOE-leading computing facilities in the country dedicated to open science.

About the Advanced Photon Source

The Advanced Photon Source (APS) Office of the U.S. Department of Energy Science at Argonne National Laboratory is one of the most productive X-ray light source facilities in the world. The APS provides high-brightness X-ray behavior to a diverse community of researchers in materials science, chemistry, thick subject physics, the life and environmental sciences, and applied research. These X-rays are ideal for the study of biological materials and structures; elemental circulation; chemical, magnetic, electrical states; and a wide range of technologically important engineering systems from batteries to fuel injection sprays, all of which are the foundations for our country’s economic, technological and physical well-being. Each year, more than 5,000 researchers use the APS to make more than 2,000 publications describing influential findings, unlocking biological protein structures more important than users of a light source search facility X -ray any other. APS scientists and engineers innovate technology that is at the heart of advancing acceleration and light source work. This includes the insertion devices that produce ultra-clear X-ray results by researchers, lenses that focus the X-rays down to a few nanometers, an instrument that magnifies the way the X-rays interact with samples being studied, and software that collects and manages the vast amount of data that comes from APS detection research.

This search used resources from the Advanced Photon Source, US DOE Science Office User Resource operated for the DOE Science Office by Argonne National Laboratory under Contract No. DE-AC02-06CH11357.

Argonne National Laboratory seeking solutions to national problems in science and technology. The country’s first national laboratory, Argonne conducts fundamental and applied scientific research at almost all scientific disciplines. Argonne researchers work closely with researchers from hundreds of federal, state, and federal companies, universities, and organizations to help them solve their unique problems, advance America’s scientific leadership and prepare the country for time a better future. With employees from more than 60 countries, Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy Science Office.

U.S. Department of Energy Office of Science is the single largest supporter of fundamental research in the physical sciences in the United States and is working to address some of the most important challenges of our time. For more information, visit https: //energy.gov /science.