Grid handling difference between fix ttm/mod and fix ttm/grid

LAMMPS LAMMPS General Discussion
1

Hello,
I am using LAMMPS version April 2021 to perform laser ablation simulation. I tried using ‘fix ttm/mod’ for this purpose and it works for small grid. But when I tried running it for larger grid the simulation becomes very slow.
As per the LAMMPS documentation, the latest version has the ‘fix ttm/grid’ option which is to be used instead of ‘fix ttm’ for large grids. But ttm/grid doesn’t have the option for providing laser parameters required for ablation simulation unlike ttm/mod.
My question is that is there any difference between ttm/grid and ttm/mod when it comes to handling the grid i.e. for a larger grid do I have to switch from ttm/mod to ttm/grid? Also, is there a way to speed up the ttm/mod computation?

Thanks
Arijit

2

You cannot switch those. Fix ttm/grid is the same model as fix ttm and thus different from fix ttm/mod.

That depends on your input and simulation settings. But the cost of increasing the number of grid points is cubic and there is nothing you can do about it, for doubling the number of grid points in each direction, you have 8 times as many grid points and the computational effort per grid point is the same.