Researchers Develop Computational Approach for Simulating Light-Matter Interactions

Researchers at the University of Tsukuba in Japan have developed a new computational approach for simulating interactions between matter and light at atomic scale. These light-matter interactions are often used to create technologies like lasers, light-emitting diodes (LEDs), and atomic clocks. However, existing computational approaches for modeling these interactions are often limited in usefulness and capability.

The new study was published in The International Journal of High Performance Computing Applications. 

Highly-Efficient Computational Method

The research describes a new highly-efficient method for simulating light-matter interactions at the atomic scale. 

One of the reasons these interactions are so difficult to simulate is that the phenomena associated with the interactions involve many different areas of physics, such as the propagation of light waves and the dynamics of electrons and ions in matter. Another challenge is that the phenomena can cover a wide range of length and time scales. 

Two Separate Methods

The multiphysics and multiscale nature of the problem means that light-matter interactions are usually modeled with two separate computational methods. The first of these methods is called electromagnetic analysis, and it involves the electromagnetic fields of the light being studied. The second is a quantum-mechanical calculation of the optical properties of the matter. 

These two methods assume that the electromagnetic fields are weak and there is a difference in the length scale.

Professor Kazuhiro Yabana is senior author of the study.

“Our approach provides a unified and improved way to simulate light-matter interactions,” says Yabana. “We achieve this feat by simultaneously solving three key physics 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 relied on their in-house software SALMON (Scalable Ab initio Light-Matter simulator for Optics and Nanoscience) to implement the method. They optimized the simulation computer code to maximize its performance before testing the code by modeling light-matter interactions in a thin film of amorphous silicon dioxide. This thin film of amorphous silicon dioxide consists of over 10,000 atoms. 

The simulation was carried out using nearly 28,000 nodes of Fugaku, which is the fastest supercomputer in the world located at the RIKEN Center for Computational Science in Kobe, Japan.

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

This new approach could be used to explore different phenomena in nanoscale optics and photonics.