TTM: parameters function of electronic temperature

Dear Lammps users,

I'am using the Two Temperatures Model in a large range of temperature in which C_e, k_e g_p and g_s widely vary.

So I would like to create variables as a function of the electronic temperature Te which will change during each time step.

variable C_e equal f(Te)
variable k_e equal f(Te)
...
fix ID group-ID ttm seed C_e rho_e kappa_e gamma_p gamma_s v_0 Nx Ny Nz T_infile N T_outfile
and of course, because Te is not the same on each mesh, the variable must be reevaluated on each mesh.

People often say they use C_e=A*tanh(B*Te) but I do not understand how they compute the formula.

I'm glad for every suggestion on how to this.

Kind regards,

Antoine

1 Like

I’m not clear if you are expecting Te to be an input to fix ttm or something

you calculation from its output. The fix ttm doc page doesn’t say anything

about variables being inputs, so you can’t do it, unless someone codes

it as an option. If you mean output, then you don’t say how you are calculating

Te. If you want to define a varaible that performs a tanh(), then LAMMPS

doesn’t have it as part of its variable syntax (see the doc page). So you’d

have to write tanh() as the sum/quotient/etc of exponentials.

Steve

Te is already an input in fix TTM.
The problem is that the other input parameters seem to be constants whereas they should be different on each mesh as a function of its electronic temperature.
So my question was "is it possible to applied this kind of input parameters in fix TTM, example: C_e=f(mesh coordinates, Te in this mesh)?"

In the publication of Duffy and Rutherford cited in the doc page , the authors write that they use this kind of function (where f=tanh) so I was expecting this to be possible...

I'm glad for every suggestion.

Antoine

I still don’t understand what you are asking. The doc pages

for fix ttm explain what inputs it allow. The 3 lines you have

posted

variable C_e equal f(Te)
variable k_e equal f(Te)

fix ID group-ID ttm seed C_e rho_e kappa_e gamma_p gamma_s v_0 Nx Ny Nz T_infile N T_outfile

are not correct LAMMPS syntax. If you tried them (have you?) you

will get an error.

I think you need to ask a more specific question about fix ttm in LAMMPS,

not about the TTM model generally (e.g. in some paper you’ve read).

Steve

Te is already an input in fix TTM.
The problem is that the other input parameters seem to be constants whereas they should be different on each mesh as a function of its electronic temperature.
So my question was "is it possible to applied this kind of input parameters in fix TTM, example: C_e=f(mesh coordinates, Te in this mesh)?"

In the publication of Duffy and Rutherford cited in the doc page , the authors write that they use this kind of function (where f=tanh) so I was expecting this to be possible...

have you read the *entire* documentation? have you noticed, that there
is a fix ttm/mod in addition to fix ttm that offers to input electron
temperature dependent parameters?

http://lammps.sandia.gov/doc/fix_ttm.html

axel.

Thank you Axel, TTM/mod is the solution to this problem.