Effective method for simulating light-matter interactions on an atomic scale

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The light-matter interaction is an essential topic that is relevant to the disciplines of physical and chemical sciences as well as optical and electrical engineering. The invention of the laser in the early 1960s led to several innovations in these areas. Since then, laser technologies have developed in different directions.

In the field of optical science, it is becoming more and more important to observe and manipulate matter at the atomic level with ultrashort pulsed light.

Light-matter interactions are difficult to simulate, since relevant phenomena for light-matter interaction are of a multiphysical nature, which include the propagation of light waves and the dynamics of electrons and ions in matter. There are three laws of physics: electromagnetism for light fields, quantum mechanics for electrons, and Newtonian mechanics for ion motion.

In one in the International Journal of. published study High performance computing applications, a research team led by the University of Tsukuba describes a highly efficient method for simulating light-matter interactions at the atomic level.

Because of the multiphysics and multiscale nature of the problem, two separate computational approaches have been developed. The first is electromagnetic analysis, which treats matter as a continuum medium, and the second is quantum mechanical ab initio computation of the optical properties of materials. These two approaches assume a light field weakness (perturbation theory in quantum mechanics) and a difference in the length scale (macroscopic electromagnetism). However, the usefulness and power of these traditional computational approaches are limited in current research.

“Our approach offers a uniform and improved way of simulating light-matter interactions.” says the lead author of the study, Professor Kazuhiro Yabana. “We achieve this feat by simultaneously solving three physical key equations: the Maxwell equation for the electromagnetic fields, the time-dependent Kohn-Sham equation for the electrons and the Newton equation for the ions.”

The researchers implemented the method in their in-house software SALMON (Scalable Ab initio Light-Matter simulator for Optics and Nanoscience). You have thoroughly tweaked the simulation computer code to maximize its performance. They then tested the code by modeling light-matter interactions in a thin film of amorphous silicon dioxide made up of more than 10,000 atoms. This simulation was performed using nearly 28,000 nodes of the world’s fastest supercomputer, Fugaku, at the RIKEN Center for Computational Science in Kobe, Japan.

“We have found that our code is extremely efficient and achieves the goal of one second per time step of the calculation, which is necessary for practical applications.” says Professor Yabana. “The performance is close to the maximum possible value, which is determined by the bandwidth of the computer memory, and the code has the desirable property of excellent weak scalability.”

Although the team in this work simulated light-matter interactions in a thin film, their approach could be used to explore many phenomena in optics and photonics on the nanoscale.

Journal reference

  1. Yuta Hirokawa, Atsushi Yamada, Shunsuke Yamada, Masashi Noda, Mitsuharu Uemoto, Taisuke Boku, Kazuhiro Yabana; Large-scale ab initio simulation of the light-matter interaction at the atomic level in Fugaku, High performance computing applications. DOI: 10.1177 / 10943420211065723
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