[Pw_forum] Problems with vc-relaxed calculation

[WANG Wei]

Vikas, I mean that the values of the the last-step (scf) calculation  are
significantly different from those of second-step calculation (vc-relax)
from bottom.  Thank you!


&control
   calculation = 'vc-relax'
!   restart_mode='from_scratch',
   prefix='graphite',
   tstress = .true.
   tprnfor = .true.
    pseudo_dir   = "/home/wangvei/works/quantum-espresso/pseudo",
    outdir       = "./",
    disk_io  = 'none'
    forc_conv_thr = 1.0e-3
/
&system
    ibrav           = 4
    celldm(1)       = 4.68
    celldm(3)       = 2.70
    nat             = 4
    ntyp            = 1
    occupations = "smearing",
    smearing    = "gaussian",
    degauss     = 0.002D0,
    ecutwfc         = 40.0
    ecutrho         = 200
!    input_dft       = 'vdw1'
/
&electrons
    conv_thr        = 1.0d-8
/
&ions
/
&cell
    press_conv_thr  = 0.5D0
    press           = 0.D0
    cell_dynamics   = 'bfgs'
/
ATOMIC_SPECIES
C   12.00   C.pbe-paw_kj.UPF
ATOMIC_POSITIONS {crystal}
 C     0.00000   0.00000   0.25000
 C     0.00000   0.00000   0.75000
 C     0.33333   0.66667   0.25000
 C     0.66667   0.33333   0.75000
K_POINTS automatic
9 9 4 0 0 0




On 2 July 2011 01:43, Vikas Varshney <vv0210 at gmail.com> wrote:

> Did you update the cell dimensions correctly? For example, if your
> celldm(1) and celldm(3) before relax are a and c. Lets say after
> relax, they become 1.1a and 1.2c. In the final scf calculation, new a
> should be 1.1a and and new c shsould be (1.2/1.1)*c.
>
> I dont know if this is the case but just wanted to tell that. Not much
> help can be done until more input is provided.
>
> Hope this helps
> Vikas
>
>
> On Fri, Jul 1, 2011 at 12:37 PM, WANG Wei <wonvein at gmail.com> wrote:
> > Dear QE users,
> >
> > Why are the total energy and press of the final step of vc-relax
> > calculation different from those of the scf calculation using the same
> > structure?  Especially for the values of press, what makes this great
> > difference between the final step of vc-relax calculation and the final
> scf
> > calculation (after the vc-relax calculation)?
> >
> > (1) For the final step of vc-relax calculation, the press and total
> energy
> > are:
> > %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
> > !    total energy              =     -73.74310183 Ry
> >
> >           total   stress  (Ry/bohr**3)                   (kbar)     P=
> > -0.03
> >   -0.00000009   0.00000001   0.00000000         -0.01      0.00      0.00
> >    0.00000001  -0.00000008   0.00000000          0.00     -0.01      0.00
> >    0.00000000   0.00000000  -0.00000048          0.00      0.00     -0.07
> > %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
> >
> > (2) For the final scf calculations, the press and total energy are:
> > %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
> > !    total energy              =     -74.60031750 Ry
> >
> >           total   stress  (Ry/bohr**3)                   (kbar)     P=
> > 638.94
> >    0.00760001  -0.00000151   0.00000000       1118.00     -0.22      0.00
> >   -0.00000151   0.00759826   0.00000000         -0.22   1117.74      0.00
> >    0.00000000   0.00000000  -0.00216804          0.00      0.00   -318.93
> > %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
> >
> > Regards,
> > WANG
> >
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> > Pw_forum at pwscf.org
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> >
> >
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