Reg. AtC Fix_flux and computational domain problem

Dear all,


I am using the user-atc package to simulate the fs laser ablation of nickel. I am struggling with an AtC problem since last three weeks. Actually I have used AtC fix_flux command to deposit about 0.3 J/cm^2 of fluence. I am getting an electron temperature (max) of about 20,000K (for computational domain of 0 10, 0 10, 0 100), that’s fine. But as soon as I increase my computational domain (to 0 20, 0 20, 0 100) then my computed electron temperature (max) found to be only 2,000-3,000K only. My question is:

  1. Am I suppose to change the flux value 388860 ((in the command fix**_modify AtC fix_flux electron temperature fcst 388860** )when I increase the computational domain increases?

  2. If not, then what else may be possible reason for the aforementioned problem?

I have taken advises from various active users, mailing lists and documentations but couldn’t find any suitable solution. Thus finally asking to to people behind the AtC programs. Kindly help me out.

Thanking you in anticipation

Vinod ​

I suggest you do the expt. Increase the flux by

the same ratio you are increasing the system size.

If the temp rise is the same, then you have your answer.


Dear Steve,

Thanks a lot for your valuable response. Experimentally It should not change by a significant number. When I tried to use “AtC source” instead of “AtC fix_flux” to deposit the input energy/fluence by femtosecond laser pulses, It did not have any effect on electron temperature (max). With “AtC source” command, electron temperature remained almost same if we increase the computational domain along x- and y-axis (when heat is influx along z-axis).

That’s why I was feeling, either there is some problem with “AtC fix_flux” command or the computed flux value what I have mentioned in the command (fix**_modify AtC fix_flux electron temperature fcst 388860**).

Does this computed flux value (388860) should increase as I increase the computational domain??

Kindly reply about this problem.

Thanking you in anticipation


The AtC folks will have to answer these Qs.


Hi Vinod, I’m sorry but I don’t have the bandwidth to dig deeply into this issue. Most of the time we’ve gotten questions like this, the underlying issue is units. Note that fluxes and sources have different units. The AtC doc page contains more details about how we compute our units as they are different from the fundamental LAMMPS units. I hope this helps.