[gmx-users] basic units: acceleration conflict

[CIHAN NADIR KAPLAN]

Dear all,

In the Gromacs manual, the basic units for length and time are given by nm(=10^-9 m) and ps(=10^-12s), respectively. When one wants to accelerate a group, he should include it in the *.mdp file in the units of nm/ps^2, which corresponds to 10^15 m/s. So , for instance, when you set the acceleration in x direction greater than ~10^-7 in the mdp file, then according to given units, it is not unphysical. Even, in order to avoid relativistic effects, it seems it should be set less than ~10^-9, but the manual says "GROMACS uses a consistent set of units that produce values in the vicinity of unity for most
relevant molecular quantities" (p.7). 

Can anyone please explain the logic behind choosing nm/ps^2 ? Any help will be greatly appreciated.

Best,
Nadir Kaplan