Dear Amir,
Well, rather the other way around: 1 2 2 in the k points, as the longer
the cell in real space, the fewer the k points needed in the corresponding
accuracy in the reci-procal space, or, the integration over the Brillouin
zone? Why? Exactly because it is the _reci-procal_ space (the longer the
real-space dimension, the shorter the one in reci-procal space, so one
needs less sampling points == k points to achieve the same
sampling distance in the integrand).
Well, I just mentioned LDA, because my first thought was that it is so
old, why not going for the GGA's plus possibly a correction for the
missing London dispersions, but at the second thought LDA is known to give
quite good results in the bulk, and it is less of the art of "fitting" the
"correct" GGA to obtain good results. Some results on the LDA versus GGA
versus other schemes were recently performed by Colleagues (my own
contribution was small but hopefully positive, ie non-destructive) in
Henri Hay et alia, Phys. Rev. B 92, 144111 DOI: 10.1103/PhysRevB.92.144111
Maybe this gives you some thoughts. I guess that if going for bulk-like
properties the GGA functionals such as PBEsol ("PBE-for-solids") might be
quite good results. It is up to you, indeed LDA might give reasonable
results, without all this fit-to-be-ab-initio-considerations of choosing
the functional to use. :) (wasntme) - just my personal opinion.
Greetings,
apsi
-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-
Ari Paavo Seitsonen / [email protected] / http://www.iki.fi/~apsi/
Ecole Normale Supérieure (ENS), Département de Chimie, Paris
Mobile (F) : +33 789 37 24 25 (CH) : +41 79 71 90 935
On Mon, 23 May 2016, Mofrad, Amir Mehdi (MU-Student) wrote:
Thank you Ari for your reply. Yes you were right about the number of atoms. It
should be 72. I figured that out too right after I sent out the email. However,
I wanted to ask about what you said at the end of your reply. So do you think 3
2 2 or even 4 2 2 would be good enough to do the optimization? Also, would you
please clarify a bit on the LDA part you mentioned?
Best,
Amir M. Mofrad
Graduate Research Assistant
Chemical Engineering Department
University of Missouri
________________________________________
From: [email protected] <[email protected]> on behalf of Ari P
Seitsonen <[email protected]>
Sent: Monday, May 23, 2016 7:18:16 AM
To: PWSCF Forum
Subject: Re: [Pw_forum] vc-relax doesn't seem to converged.
Dear Amir,
Did you check your geometry, for example visually (XCrysDen, VESTA,
...)? To me it looks as if there are some Si atoms missing in the
structure, and thus there are dangling bonds on oxygens. Was this your
purpose?
In principle you can later change your k point sampling in the direction
corresponding to the long axis of the unit cells. LDA, hmm, well if you
want. :)
Greetings from Paris,
apsi
-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-
Ari Paavo Seitsonen / [email protected] / http://www.iki.fi/~apsi/
Ecole Normale Supérieure (ENS), Département de Chimie, Paris
Mobile (F) : +33 789 37 24 25 (CH) : +41 79 71 90 935
On Thu, 19 May 2016, Mofrad, Amir Mehdi (MU-Student) wrote:
Dear all QE users and developers,
So far I have been doing scf calculations on one unit cell of a specific type
of zeolite (which is called SOD) and I have been
getting some good results. However, recently I wanted to extend my calculations
on more than one unit cell (2x1x1 for
instance). The problem is when I do vc-relax it does not optimize the cell nor
the internal coordinates of atoms. I put my
input file in case you might need to take a look at. Any help would be
thoroughly appreciated.
&CONTROL
calculation = 'vc-relax' ,
restart_mode = 'from_scratch' ,
wf_collect = .true. ,
outdir = './scratch' ,
wfcdir = './scratch' ,
pseudo_dir = '/global/espresso/pseudo' ,
prefix = 'SOD' ,
verbosity = 'high' ,
etot_conv_thr = 1e-5 ,
forc_conv_thr = 1e-4 ,
nstep = 50 ,
tstress = .true. ,
tprnfor = .true. ,
/
&SYSTEM
ibrav = 0,
nat = 70,
ntyp = 2,
ecutwfc = 31 ,
ecutrho = 310 ,
/
&ELECTRONS
electron_maxstep = 100,
conv_thr = 3e-8 ,
mixing_mode = 'plain' ,
mixing_beta = 0.7 ,
diagonalization = 'david' ,
/
&IONS
ion_dynamics = 'bfgs' ,
trust_radius_ini = 0.5 ,
/
&CELL
cell_dynamics='bfgs',
cell_factor=5,
/
CELL_PARAMETERS angstrom
18.0000 0.00000 0.00000
0.00000 9.00000 0.00000
0.00000 0.00000 9.00000
ATOMIC_SPECIES
Si 28.08600 Si.pz-n-rrkjus_psl.0.1.UPF
O 15.99940 O.pz-n-rrkjus_psl.0.1.UPF
ATOMIC_POSITIONS angstrom
O 1.31516 4.48250 7.64983
Si 2.24125 4.48250 0.00000
O 4.48250 1.31517 7.64983
O 7.64983 4.48250 7.64983
O 4.48250 7.64983 7.64983
O 1.31517 4.48250 1.31517
O 4.48250 1.31517 1.31517
O 7.64983 4.48250 1.31517
O 4.48250 7.64983 1.31517
O 7.64983 1.31517 4.48250
O 7.64983 7.64983 4.48250
O 1.31516 7.64983 4.48250
O 1.31517 1.31517 4.48250
O 5.79767 -0.00000 3.16733
O -0.00000 5.79767 3.16733
O 3.16733 -0.00000 3.16733
O -0.00000 3.16733 3.16733
O 5.79767 -0.00000 5.79767
O -0.00000 5.79767 5.79767
O 3.16733 -0.00000 5.79767
O -0.00000 3.16733 5.79767
O 3.16733 5.79767 0.00000
O 3.16733 3.16733 0.00000
O 5.79767 3.16733 0.00000
O 5.79767 5.79767 0.00000
Si 4.48250 2.24125 0.00000
Si 6.72375 4.48250 0.00000
Si 4.48250 6.72375 0.00000
Si -0.00000 2.24125 4.48250
Si 6.72375 -0.00000 4.48250
Si -0.00000 6.72375 4.48250
Si 2.24125 -0.00000 4.48250
Si 4.48250 -0.00000 2.24125
Si -0.00000 4.48250 2.24125
O 10.28017 4.48250 7.64983
Si 11.20625 4.48250 0.00000
O 13.44750 1.31517 7.64983
O 16.61483 4.48250 7.64983
O 13.44750 7.64983 7.64983
O 10.28017 4.48250 1.31517
O 13.44750 1.31517 1.31517
O 16.61483 4.48250 1.31517
O 13.44750 7.64983 1.31517
O 16.61483 1.31517 4.48250
O 16.61483 7.64983 4.48250
O 10.28017 7.64983 4.48250
O 10.28017 1.31517 4.48250
O 14.76267 -0.00000 3.16733
O 8.96500 5.79767 3.16733
O 12.13233 -0.00000 3.16733
O 8.96500 3.16733 3.16733
O 14.76267 -0.00000 5.79767
O 8.96500 5.79767 5.79767
O 12.13233 -0.00000 5.79767
O 8.96500 3.16733 5.79767
O 12.13233 5.79767 0.00000
O 12.13233 3.16733 0.00000
O 14.76267 3.16733 0.00000
O 14.76267 5.79767 0.00000
Si 13.44750 2.24125 0.00000
Si 15.68875 4.48250 0.00000
Si 13.44750 6.72375 0.00000
Si 8.96500 2.24125 4.48250
Si 15.68875 -0.00000 4.48250
Si 8.96500 6.72375 4.48250
Si 11.20625 -0.00000 4.48250
Si 13.44750 -0.00000 6.72375
Si 8.96500 4.48250 6.72375
Si 13.44750 -0.00000 2.24125
Si 8.96500 4.48250 2.24125
K_POINTS automatic
2 2 2 1 1 1
Best,
Amir M. Mofrad
University of Missouri
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