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["matthieu verstraete" <matthieu.jean.verstraete@gmail.com>]

As Pierre-Matthieu said, we need more information to be accurate, but a few months ago something like this was discussed on the forum: it is probable that you have changed the ecutsm or dilatmx parameters between your 2 runs. This changes
1) the actual spheres of G vectors used
2) the contribution of the last G vectors (with ecutsm their contribution goes smoothly to 0 for the last shell)

both of these will affect the energy and stress calculated. If you are well converged then the contribution from the last shells of G should be negligible, but usually this is not the case. Try to repeat your 2nd calculation with the exact same ecutsm and dilatmx (and ecut of course) to see if it improves agreement. Also, you should try to exhaust the convergence, to see if you are close to the correct value.

Matthieu

On Mon, Jan 19, 2009 at 8:27 AM, Anglade Pierre-Matthieu <anglade@gmail.com> wrote:

Hi,

It is quite likely possible to help you. However, to proceed, one would need : both of your input file and relevant part of the relaxation output file.
Do you consider possible that your calculation parameters were unconverged ? Or that your scf/non-scf loops were unconverged ?

regards

PMA

On Mon, Jan 19, 2009 at 6:38 AM, kong <kongl@physics.rutgers.edu> wrote:

Hi,

I relaxed a system using optcell =2 and ionmov=3. After the desired convergence
is achieved, I copied the relaxed lattice parameters( acell/angles) and
atomic positions(xangst)  from the output file and start a new calculation
without
relaxation. All the other input variables are same as before.  I am very
surprised
that the new total energy is about 0.2Ha lower than  the relaxed results,
but the stress tensor is three order of magnitude larger!

I note that ngfft/boxcut(ratio) in the relaxation is different. But using the
same ngfft(which also leads to the same boxcut(ratio)) in the input file does
not improve the consistency.
Would anyone help me out on it? Thanks!

Lingzhu

--
Pierre-Matthieu Anglade

-- 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Dr. Matthieu Verstraete

European Theoretical Spectroscopy Facility (ETSF) 
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Mail : matthieu.jean.verstraete@gmail.com
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