[Pw_forum] VC-Relaxation

[Diep Vinh Quang]

Dear Axel,

Thank you very much for your reply, I change the input file a little bit
(by inscrease nstep=100 (instead of 50) and the outdir='/tmp') but  I
still get the error. The error message is "FORTRAN STOP 2" (and for sure
it run longer than the previous one). But the result is reasonable when i
checked separately by the SCF method. I mean after getting the results
from the VC-relaxation (with Stop after sometime), using that result as an
input for "scf" and the total energy is very good in the sensen that is
agree very well with other calculation.

Thank you very much.

Vinh



>
> On Fri, 1 Jul 2005, Diep Vinh Quang wrote:
>
> VQ> Hi all,
>
> hi vinh,
>
> VQ> How can we using the Variable Cell Relaxation programe. I have the
>
> please have a look at the Doc/INPUT_PW file of the espresso distribution,
> it should have a lot of useful information about the various flags
> and parameters. the only are a little scattered throughout the file.
>
> VQ> following input file for pw.x but after some time, the propram stop.
> And
>
> was there an error message, or did the program just stop?
>
> VQ> on the other hand, how can we fix the pressure for the cell. did i do
> the
> VQ> right thing in the following input? (Does it means the pressure acting
> on
> VQ> the cell after minimization =12.8 kba?)
>
> that should be written in the output.
>
> VQ>
> VQ> &control
> VQ>     calculation = 'vc-relax'
> VQ>     restart_mode='from_scratch',
> VQ>     prefix='Polyethylene',
> VQ>
> VQ>     tstress = .true.
> VQ>     tprnfor = .true.
> VQ>   pseudo_dir =
> VQ> '/afs/ictp.trieste.it/home/v/vdiep/espresso-2.1.3/Polyethylene/',
> VQ>
> outdir='/afs/ictp.trieste.it/home/v/vdiep/espresso-2.1.3/Polyethylene/'
>
> hmmm... it probably is not a good idea to use AFS for
> storing your scratch files. running a job with pw.x may create a
> substantial amount of i/o and you ideally want to keep that
> on a local scratch disk. actually, you should also check whether
> the job stops, because you're running out of disk quota.
>
> VQ>  /
>
> also you don't specify a value for nstep. perhaps
> your job just stopped becaus it reached the default
> limit of 50(?) ionic steps.
>
> VQ>  &system
> VQ>      ibrav=8,
> VQ>                     celldm(1) = 13.48016706
> VQ>                     celldm(2) = 0.7173398007
> VQ>                     celldm(3) = 0.3609829952
> VQ>     nat=12 , ntyp= 2,
> VQ>     ecutwfc =40.0,
>
> hmmm. for a variable cell calculation with ultra-soft pseudopotentials,
> you may have to also increase the density cutoff here from the default
> 4*ecutwfc. i remember there were some discussions about that, please
> check the mailing list archive.
>
> hope this helps,
> 	axel.
>
>
> --
>
> =======================================================================
> Dr. Axel Kohlmeyer   e-mail: axel.kohlmeyer at theochem.ruhr-uni-bochum.de
> Lehrstuhl fuer Theoretische Chemie          Phone: ++49 (0)234/32-26673
> Ruhr-Universitaet Bochum - NC 03/53         Fax:   ++49 (0)234/32-14045
> D-44780 Bochum  http://www.theochem.ruhr-uni-bochum.de/~axel.kohlmeyer/
> =======================================================================
> If you make something idiot-proof, the universe creates a better idiot.
>


-------------------------------------------------
Diep Vinh Quang
C/o Diploma Program, The Abdus Salam
International Center for Theoretical Physics(ICTP),
11 Strada Costiera, 34014, Trieste,Italy.
http://www.ictp.it