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Bigger Steps: Berkeley Lab Researchers Develop Algorithm to Make Simulation of ­ltrafast Processes Possible

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Model of ion (Cl) collision with atomically thin semiconductor (MoSe2).

A new algorithm developed by researchers at Lawrence Berkeley National Laboratory increased the small time step required to create real-time simulations of ultrafast phenomena.

Credit: Lawrence Berkeley National Laboratory

Lawrence Berkeley National Laboratory researchers have developed an algorithm that increases the small time step, which is required to create the real-time simulations of ultrafast phenomena such as describing the movement of an electron, from about one attosecond to about half a femtosecond.

The researchers say their breakthrough enables them to simulate ultrafast phenomena for systems of about 100 atoms. "We demonstrated a collision of an ion with a [two-dimensional] material for 100 femtoseconds," which represents a reduction from 100,000 time steps down to only 500, according to Berkeley Lab researcher Lin-Wang Wang.

An excited system can be modeled, using real-time simulations, with time-dependent quantum mechanical equations that describe the movement of electrons. The new algorithm expands equations into individual terms, based on which states are excited at a given time. The key is to determine the time evolution of the individual terms.

"By eliminating higher energy terms, you significantly reduce the dimension of your problem, and you can also use a bigger time step," Wang says.

He notes solving the equations in bigger time steps reduces the computational cost and increases the speed of simulations.

From Lawrence Berkeley National Laboratory
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