Hello, I am a student who has just started learning about ttm/mod, and the discussion above has been very helpful for me as a beginner—thank you very much. However, I still have a question. I would like to simulate ultrafast laser irradiation on a one-dimensional metal target, just like the schematic you initially provided. But when I set surface_movement to 1, in the very first timestep of the simulation, all the electron grid points that were initially set as vacuum (0 K) were assigned the minimum electron temperature in the electron temperature output file. Then I set surface_movement to 0, but in this case, the atoms no longer diffuse into the vacuum region, making it impossible to reproduce the results from the literature. May I ask if you have any insights into this issue now?