Shuangxing Dai wrote:
Hi, all,
I was wondering why I got large pressure after energy
minimization. In MD, the pressure and pressure tensor is defined like (
equation 4.151 in manual):
P=2*(E_kinetic + W)/(3*V), V is volume and W is Virial.
I run a simple system, fcc gold with LJ potential to check the pressure
after energy minimization. I got:
There are no velocities, so whatever is computed here is not the pressure.
Pressure (bar)
8.75158e+03
Steepest Descents converged to Fmax < 1 in 1 steps
Potential Energy = -1.4870625e+03
Maximum force = 2.2925207e-05 on atom 1606
Norm of force = 7.9803776e-06
The force is very small and the energy minimization finished in 1 steps,
since all the atoms are at equilibrium. So I was wondering why I got
this huge pressure. And in a lot of simulations, I found huge pressure
after energy minimization. Even in free energy tutorial on Wiki, I found
large pressure as larege as 1 GPa.
See http://oldwiki.gromacs.org/index.php/Pressure
After energy minimization, the forces
are very small and no velocity, so the pressure should be close to zero.
Anyone has any idea about this?
I guess it should not be computed.
PS: Why the forces in traj.trr are all zeros?
EM doesn't write forces.
Mark
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