Overdamped vs underdamped Langevin

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SUMMARY

The discussion focuses on the formulation of overdamped and underdamped Langevin equations. The overdamped equation is presented as \(\dot{x}_i=x_{i+1}+x_{i-1}-2x_i-V'(x_i)+F(t)\), while the underdamped equation is expressed as \(\ddot{x}_i+\gamma\dot{x}_i=\gamma x_{i+1}+\gamma x_{i-1}-2 \gamma x_i-\gamma V'(x_i)+\gamma F(t)\). The participants confirm that the damping parameter \(\gamma\) has been absorbed into the terms, suggesting that it can redefine the length scale. The discussion also highlights the need for more information about the physical system to provide further insights.

PREREQUISITES
  • Understanding of Langevin dynamics
  • Familiarity with differential equations
  • Knowledge of damping parameters in physical systems
  • Basic concepts of particle interactions and nearest neighbors
NEXT STEPS
  • Research the derivation of Langevin equations in statistical mechanics
  • Explore the differences between overdamped and underdamped regimes
  • Study the impact of damping parameters on particle dynamics
  • Review relevant literature on Langevin dynamics, such as the paper linked in the discussion
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Physicists, researchers in statistical mechanics, and students studying particle dynamics will benefit from this discussion, particularly those interested in Langevin equations and their applications in modeling physical systems.

LagrangeEuler
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If overdamped equation looks like
##\dot{x}_i=x_{i+1}+x_{i-1}-2x_i-V'(x_i)+F(t)##
How to write down the underdamped Langevin equation
##\ddot{x}_i+\gamma\dot{x}_i=\gamma x_{i+1}+\gamma x_{i-1}-2 \gamma x_i-\gamma V'(x_i)+\gamma F(t)##
Am I right?
 
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It does look like the ##\gamma## has been absorbed into the terms. But I guess it could have been used to redefine the length scale, so I'm sure that multiplying everything by ##\gamma## is the right thing to do. You have to go back to the derivation of the equation.

And what does the index ##i## stand for?
 
It labels particles. For example particle ##i## has neirest neighbours ##i-1## and ##i+1##.
 
LagrangeEuler said:
It labels particles. For example particle ##i## has neirest neighbours ##i-1## and ##i+1##.

Then I really need more information on the physical system you are considering before I can be of any help.
 
http://allariz.uc3m.es/~anxosanchez/ep/prb_50_9652_94.pdf
 
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Looking at equation (1) in that paper, they have the damping parameter ##\alpha##. I skimmed through the article, and couldn't find any indication that they are considering an overdamped regime, or indeed the first equation you gave in the OP.
 
I known. But I'm interesting in that relation. Do you know some reference where I can find it? How could you always get from overdamped, underdamped and vice versa?
 

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