Lennard Jones- reduced units

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MD simulation with a Lennard Jones potential to the value for a different substance with different e and sigma parameters. This is because MD simulations use reduced units and there is a law of corresponding states that may allow for this conversion without having to run a separate simulation for each substance. However, it's important to note that one simulation is only valid for one state defined by temperature and density, so there is no direct way to extrapolate the results to other states. In summary, Ronald is asking if the law of corresponding states can be used to convert thermodynamic quantities calculated for one substance in MD simulation to those of another substance with different parameters, but
  • #1
ronbenin
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Hi friends,
I have a question regarding MD simulation using a LJ potential. If I take the e and sigma parameters in the LJ potential to be that corresponding to argon, and calculate some thermodynamic
quantity can I convert the value of that thermodynamic quantity corresponding to some other substance
which might have a different e and sigma. This is because in MD simulation we use reduced units and there is something called the law of corresponding states which might enable one to convert that thermodynamic quantity for another substance without having to run a different simulation.

Please help.

Thanks,
Ronald
 
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  • #2
Welcome to Physics Forums!
Let's say that at certain temperature and density (T1, rho1)you calculate certain quantities for Ar. Then these quantities also belong to Xe at another temperatue and density (T2,rho2) and also belong to Kr at third T,rho and for all other materials decribed by Lennard Jones at Different T,rho.
However, keep in mind that one simulation is equivalent to one state defined by T,rho. There is no direct way to extrapolate the results of one simulation to other states.
 
  • #3
Hi,
thanks a lot for your help.

Ronald
 

What are Lennard Jones-reduced units?

Lennard Jones-reduced units are a system of units commonly used in molecular simulations and statistical mechanics calculations. They are a way of representing physical quantities such as energy, length, and temperature in a dimensionless form, making them easier to work with and compare across different systems.

Why are Lennard Jones-reduced units used?

Lennard Jones-reduced units are used because they simplify calculations in molecular simulations and statistical mechanics. By removing the need for physical units, they allow for easier comparison between different systems and eliminate the need for unit conversions.

How are Lennard Jones-reduced units defined?

Lennard Jones-reduced units are defined by setting the Lennard-Jones parameters, sigma and epsilon, to 1. This results in the unit of length being equal to sigma, the unit of energy being equal to epsilon, and the unit of temperature being equal to epsilon/kB, where kB is the Boltzmann constant.

What is the advantage of using Lennard Jones-reduced units in simulations?

The advantage of using Lennard Jones-reduced units in simulations is that they simplify calculations and allow for easier comparison between different systems. This can save time and reduce errors in simulations, as well as provide a more intuitive understanding of the system being studied.

Are Lennard Jones-reduced units used in all simulations?

No, Lennard Jones-reduced units are not used in all simulations. They are most commonly used in molecular simulations and statistical mechanics calculations, but may not be applicable or necessary in other types of simulations.

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