[Pw_forum] time of scf and nscf computations

[Mike Klymenko]

Thank you very much for fast response! Below is a piece of my bash script
doing both calculations. Could the reason of such a behavior be due to the
option "automatic" in k-points setting?

#########################################################################

# self-consistent calculation
    cat > si.scf.in << EOF
 &control
    calculation = 'scf'
    restart_mode='from_scratch',
    prefix='silicon',
    tstress = .true.
    tprnfor = .true.
    pseudo_dir='/QEfiles/pure_Si/',
    outdir='/QEfiles/pure_Si/'
 /
 &system
    ibrav=  2, celldm(1) =10.20, nat=  2, ntyp= 1,
    ecutwfc =18.0
 /
 &electrons
 /
ATOMIC_SPECIES
 Si  28.086  Si.pz-vbc.UPF
ATOMIC_POSITIONS
 Si 0.00 0.00 0.00
 Si 0.25 0.25 0.25
K_POINTS(automatic)
 4 4 4 0 0 0
EOF

echo -e "running the scf calculation for Si ... \c"
$PW_COMMAND < si.scf.in > si.scf.out
echo "done!"


# non-self-consistent calculation
    cat > si.nscf.in << EOF
 &control
    calculation = 'nscf'
    restart_mode='from_scratch',
    prefix='silicon',
    tstress = .true.
    tprnfor = .true.
    pseudo_dir='/QEfiles/pure_Si/',
    outdir='/QEfiles/pure_Si/'
 /
 &system
    ibrav=  2, celldm(1) =10.20, nat=  2, ntyp= 1,
    ecutwfc =18.0
 /
 &electrons
ATOMIC_SPECIES
 Si  28.086  Si.pz-vbc.UPF
ATOMIC_POSITIONS
 Si 0.00 0.00 0.00
 Si 0.25 0.25 0.25
K_POINTS(automatic)
 4 4 4 0 0 0
EOF

echo -e "running the nscf calculation for Si ... \c"
$PW_COMMAND < si.nscf.in > si.nscf.out
echo "done!"

#################################################################3

Sincerely,
Dr. Mykhailo Klymenko
------------------------------------------------------------------------------------------
Universite de Liège,
Chimie Physique Théorique, Bat. B6c,
Allée du 6 aout, 11
B-4000 Sart Tilman, Liège
Belgium


2013/9/28 Paolo Giannozzi <paolo.giannozzi at uniud.it>

> On Fri, 2013-09-27 at 20:11 +0200, Mike Klymenko wrote:
> > I am an beginner in QE computing,and I am curious whether it is ok,
> > that the computational time for nscf task is much longer than the one
> > for scf job, even though I set exactly the same parameters for both of
> > then including k-space sampling. Thank you!
>
> in principle, non-scf is faster. In practice, there isn't a
> large difference. It seems to me very strange that a non-scf
> calculation performed under exactly the same conditions is
> much slower than the scf one
>
> P.
>
>
> --
> Paolo Giannozzi, Dept. Chemistry&Physics&Environment,
> Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
> Phone +39-0432-558216, fax +39-0432-558222
>
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