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Related Concept Videos

Instantaneous Power01:22

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Instantaneous power is important in electrical circuits, mainly when dealing with sinusoidal input. Instantaneous power, denoted as p(t), results from the multiplication of the instantaneous voltage (v(t)) across an element and the instantaneous current (i(t)) flowing through it. This relationship adheres to the passive sign convention and represents a fundamental principle in electrical engineering.
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Acceleration is in the direction of the change in velocity, but it is not always in the direction of motion. When an object slows down, its acceleration is opposite to the direction of its motion. Although commonly referred to as deceleration, this causes confusion in our analysis as deceleration is not a vector, and does not point to a specific direction with respect to a coordinate system. Therefore, the term deceleration is not used. For example, when a subway train slows down, it...
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The total change in the motion of an object is proportional to the total force vector acting on it and the time over which it acts. This product is called impulse, a vector quantity with the same direction as the total force acting on the object.
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The average velocity during a time interval cannot tell us how fast or in what direction a particle is moving at any given time during the interval. To calculate this, it is important to know the instantaneous velocity, which is the velocity at a specific instant of time or at a specific point along the path. Instantaneous velocity is the quantity that measures how fast an object is moving along its path. In other words, the instantaneous velocity vx of an object is the limit of the average...
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Cooling an Optically Trapped Ultracold Fermi Gas by Periodical Driving
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Nonadiabatic ImF instanton rate theory.

Rhiannon A Zarotiadis1,2,3, Jeremy O Richardson1

  • 1Department of Chemistry and Applied Biosciences, ETH Zürich, 8093 Zürich, Switzerland.

The Journal of Chemical Physics
|February 24, 2026
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Summary
This summary is machine-generated.

Semiclassical instanton theory, crucial for nuclear quantum effects in reactions, has been refined. A new nonadiabatic theory accurately captures tunneling and high-temperature limits, improving upon previous methods.

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Area of Science:

  • Quantum Chemistry
  • Chemical Dynamics
  • Theoretical Chemistry

Background:

  • Semiclassical instanton theory models nuclear quantum effects like tunneling in chemical reactions.
  • Existing nonadiabatic rate theories often rely on the less rigorous ImF premise, failing to bridge key limits.
  • Recent work established a rigorous flux-correlation function framework for nonadiabatic rate theory.

Purpose of the Study:

  • To critically examine previous ImF-based nonadiabatic rate theories.
  • To develop a new nonadiabatic ImF rate theory addressing limitations of prior methods.
  • To analyze the new theory's performance across different coupling and temperature regimes.

Main Methods:

  • Analysis of existing ImF-based semiclassical instanton theories.
  • Development of a novel nonadiabatic ImF rate theory.
  • Testing the new theory on asymmetric and multidimensional models, including deep tunneling and high-temperature limits.

Main Results:

  • Previous ImF-based theories, including mean-field ring-polymer instanton theory, were found to incorrectly capture the Born-Oppenheimer and golden-rule limits.
  • The newly developed nonadiabatic ImF theory shows reliable results for deep tunneling.
  • Limitations were observed for the high-temperature rate theory aspect of the new model.

Conclusions:

  • Previous ImF-based nonadiabatic rate theories have significant shortcomings in bridging key theoretical limits.
  • The new nonadiabatic ImF theory offers improvements, particularly for deep tunneling phenomena.
  • Further development is needed to address limitations in high-temperature nonadiabatic rate theory and its application in molecular dynamics.