The University of Bayreuth's physicists are among the world's pioneers of power functional theory. For the first time, this novel method allows researchers to precisely explain the dynamics of many-particle systems throughout time. Atoms, molecules, and bigger particles that are invisible to humans are examples of particles. The new theory broadens the scope of the traditional density functional theory, which is limited to many-particle systems in thermal equilibrium. A research team led by Prof. Dr. Matthias Schmidt presents the main aspects of the theory, which was extensively refined and elaborated at Bayreuth, in Reviews of Modern Physics.
When
the temperature in a many-particle system is balanced and no heat flows, it is
said to be in thermal equilibrium. This does not imply that the system is in a
state of strict rest. A lottery draw machine, which rotates at a consistent
pace, can be comparable to several many-particle systems. The balls have a lot
of freedom of movement and hop around in an unorganised manner. The particles
in a fluid many-particle system are packed much more tightly than in a drum,
which is why they constantly collide at small distances and time intervals. The
density functional theory may thoroughly and exactly describe the essential
features of such systems, assuming that the system is in thermal equilibrium.
In
the case of the lottery draw mechanism, this equilibrium is broken when the
uniform rotation slows down and the chamber reverses direction. The winning
numbers are then rolled onto a rail within the chamber and eventually ejected.
The power functional theory is required to accurately and without gaps record
such processes: it puts the winners' luck into the language of physics.
"The
classical density functional theory is a very detailed and appealing theory at
the same time. It may describe and relate the many complicated processes that
occur in a system when it is in thermal equilibrium. Phase transitions,
crystallizations, and phenomena like hydrophobicity, which occurs when surfaces
or particles avoid contact with water, are examples of these processes. Such
processes are frequently of tremendous technological or biological importance.
For the past ten years, we have been looking for ways to make many-particle
systems in thermal disequilibrium accessible to an equally precise and elegant
physical description in Bayreuth, thanks to the elegance and power of density
functional theory. Important studies from research partners at the University
of Fribourg in Switzerland have aided in this effort. Prof. Dr. Matthias
Schmidt, who holds a chair in theoretical physics at the University of
Bayreuth, says, "For example, our collaborative efforts have resulted in
power functional theory, which extends density functional theory to
time-dependent processes."
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