Fix ttm parameter evaluation


I’m trying to implement the fix ttm module for track formation due to heavy ion irradiation. I have a particular question about how to obtain the friction coefficient due to electron stopping, gamma_s. The easiest method is to use the SRIM table and get the electron-stopping value which has a unit of eV/A. How do I convert that to gamma_s units (mass/time)?
I looked up the literature “D M Duffy and A M Rutherford, J. Phys.: Condens. Matter, 19, 016207-016218 (2007)”, there is a formula for gamma_s which is as below
Screenshot 2023-07-02 at 1.23.24 PM
But here, the gs has a unit of W/m^3/K. Can anyone help me with this problem?


Hi @farshidreza105,

You are focusing on a simple dimensional analysis problem but the values used for \gamma_s are given just below in the paper. This is not a LAMMPS related issue.

HI @Germain,

Thanks for replying back to me. I understand that the use of \gamma_s is given in the paper after the equations. And the equation is given as
\frac{dE}{dX}=\lambda E^{1/2}
But the problem is that it explicitly says that this model is valid for low energy regime. And, additionally, they don’t mention anything about how to obtain \lambda from SRIM. Can you help me in this regard?

This is something that you should deal with with the help of a colleague or advisor that knows the literature and what you are trying to simulate better than random people on the internet. Directly contacting authors that published using the two temperature model might be an alternative.

Maybe the model is valid in what you’re trying to achieve, maybe it is not. That I can’t tell.

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Thanks for the suggestion!