is the energy decreasing ? if so the relaxation is not yet finished.
stefano
On 18/02/2018 02:55, Hind Almisbahi wrote:
Dear experts of quantum espresso,
I am doing relaxation and the problem is that the total force is
decreasing until the 4^th scf, then start to increase gradually. The
system does not converge. Actually, I need to calculate the band
structure and see the band gap of Armchair graphene ribbon. The ribbon
width is composed of 17 carbon atoms (N=3p+2 family), so it is
metallic. I have one unit cell of the ribbon. I read in this mailing
list many useful discussions about suitable input for metallic systems
and I followed them as I understand. The version of quantum espresso
is 6.1.
I tried many options of the input script but all the runs have the
same problem, total force is decreasing until the 4^th scf then start
to increase gradually. This is a complete version of my input:
&CONTROL
calculation='relax',
outdir='.\Work',
prefix='Arm17',
pseudo_dir='C:\qe-6.1\pseudo',
verbosity='high',
etot_conv_thr= 1.0D-3,
forc_conv_thr=1.0d-2,
/
&SYSTEM
ibrav=8,
a=41.1089d0,
b=4.26258d0,
c=20.0d0,
nat=34,
ntyp=1,
ecutwfc=65,
ecutrho=520,
nbnd=76
occupations='smearing',
smearing='marzari-vanderbilt',
degauss=0.001d0,
/
&ELECTRONS
conv_thr=1d-06,
mixing_beta=0.7d0,
mixing_mode='local-TF'
mixing_ndim=12
diagonalization='cg'
/
&IONS
/
ATOMIC_SPECIES
C 12.010700d0 C.pbe-rrkjus.UPF
ATOMIC_POSITIONS {crystal}
C0.0336555229d00.6666666956d00.5000000000d0
C0.0919486003d00.8333333913d00.5000000000d0
C0.0336555229d00.3333333044d00.5000000000d0
C0.1502416777d00.6666666956d00.5000000000d0
C0.2085347551d00.8333333913d00.5000000000d0
C0.0919486003d00.1666666087d00.5000000000d0
C0.1502416777d00.3333333044d00.5000000000d0
C0.2668277852d00.6666666956d00.5000000000d0
C0.3251206731d00.8333333913d00.5000000000d0
C0.2085347551d00.1666666087d00.5000000000d0
C0.2668277852d00.3333333044d00.5000000000d0
C0.3834141768d00.6666666956d00.5000000000d0
C0.4417072068d00.8333333913d00.5000000000d0
C0.3251206731d00.1666666087d00.5000000000d0
C0.3834141768d00.3333333044d00.5000000000d0
C0.5000002369d00.6666666956d00.5000000000d0
C0.5582932669d00.8333333913d00.5000000000d0
C0.4417072068d00.1666666087d00.5000000000d0
C0.5000002369d00.3333333044d00.5000000000d0
C0.6165862969d00.6666666956d00.5000000000d0
C0.6748793269d00.8333333913d00.5000000000d0
C0.5582932669d00.1666666087d00.5000000000d0
C0.6165862969d00.3333333044d00.5000000000d0
C0.7331723570d00.6666666956d00.5000000000d0
C0.7914653870d00.8333333913d00.5000000000d0
C0.6748793269d00.1666666087d00.5000000000d0
C0.7331723570d00.3333333044d00.5000000000d0
C0.8497584170d00.6666666956d00.5000000000d0
C0.9080514470d00.8333333913d00.5000000000d0
C0.7914653870d00.1666666087d00.5000000000d0
C0.8497584170d00.3333333044d00.5000000000d0
C0.9663444771d00.6666666956d00.5000000000d0
C0.9080514470d00.1666666087d00.5000000000d0
C0.9663444771d00.3333333044d00.5000000000d0
K_POINTS {automatic}
150 1 0 0 0
These are some of the many options that I have explored:
The above potential is ultrasoft, I used also norm conserving
(C.pbe-mt_gipaw.UPF).
Smearing: I used methfessel-paxton and marzari-vanderbilt
Degause: I used 0.01 and 0.001
mixing_beta: I used 0.1 and 0.7
mixing_mode: I used local-TF and TF
mixing_ndim: I used 8 and 12
diagonalization: I used cg and david
ecutwfc: I used 65 and 75
ecutrho: with norm conserving (ecutwfc*4 and ecutwfc*10), with
ultrasoft (ecutwfc*8)
nbnd=76 (I have 34 atoms, so 136 valence electrons which need 68
bands, because it is metallic I added 8 extra bands)
Previously I have successfully calculated the band structure and band
gap of semiconductor ribbon but I could not do the calculation of
metallic ribbon. I appreciate any help to solve my problem, why the
forces always increase after the 4^th scf?
Best Regards,
Hind
Lecturer, IT department
King Abdulaziz University
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