Hi all,
We have an old input script in LJ units with charges that we started using again recently, but now it spends 97% of the time in kspace (it used to work fine in 2011). The 2 Mar 2012 LAMMPS update was related to kspace and it says:
“BACKWARD COMPATIBILITY issues: Specifying a PPPM relative precision such as 1.0e-4 for the kspace_style command will give the same results as before for “real”, “lj”, and “metal” units. However, it will induce a different grid for “si,” “cgs”, and “electron” units. …”
However, we seem to be getting a different grid even though we’re in LJ units.
In older versions of LAMMPS, our kspace grid was 72x72x72, while in the newer version it is 150x150x150. An equivalent grid (and similar performance) can be obtained by using a relative error of 3e-3 instead of the typical 1e-4. Increasing the coul/long cutoff by a factor of 2 also gives the same grid size (with same rel error of 1e-4) but is obviously less efficient.
Am I missing something?
I’ve attached a simple script and smaller input file. Using these, the simulation time is 73% due to kspace using LAMMPS from 12 Feb 2012 and then 95% of time in kspace using LAMMPS from 28 May 2012.
Best,
Lisa
inputtest.lammps (2.07 KB)
LMHinputscript (1.34 KB)