[QE-users] oscillating pressure during vc-relax

[Matthew Marcus]

I'm doing a relaxation now and find that the pressure oscillates by +-0.5kbar or so with a period of maybe 6 iterations.  The oscillation doesn't damp out
quickly so it's taking forever to converge.  It's a structure with 104 atoms run on an old Linux box with 8 processors (I'm using 7 to be safe), so it's been
4 days and still going.
Is there interesting physics behind the oscillation?  Is there a parameter which could be tuned to make it converge faster?

My strategy is to pick reasonable values for the convergence parameters, relax the structure, then converge the relaxed structure and re-relax it if
I find that I need to use different parameters than the ones I guessed.  The idea is that the convergence tests are best performed on something close to
the actual system, which I take to mean with the atoms in more or less the right places.  Does this make sense?
-- 
Sincerely,
     Matthew Marcus