I want to carry out simulations in LAMMPS for a metallic system.
I am confused as to how to choose the reduced time step.
The unit of time, tau, is tau=sqrt(masssigmasigma/epsilon).
If I want a time-step of 1 femto-second, I will get
different values of the reduced time-step depending on different
values of tau.
For, example, if I choose mass=1 amu, sigma =1 Angstrom
and epsilon =1 ev, I get a reduced time-step 0.1 for 1 femtosecond.
However, if I choose the actual mass of the metal (copper), i.e
63.546 amu, and if I chose sigma to be the value at which the potential
crosses the zero axis, i.e. about 2 Angstrom, and epsilon to be
about 0.1ev, then I get a much lower value for the reduced time-step,
which corresponds to 1 femtosecond.
Is there any rule on how to choose the reduced time-step.