Dear A Suresh,
My standard answer, sorry for that - did you check that the value of
'ecutwfc' is sufficient? In the Good Old Days (at FHI) we used to use
something more like 80-100 Ry for FHI-pseudos of oxygen, and that in
ionc relaxations-only: The 'vc-relax' requires yet-a higher value. Did you
try to start a new calculation from the lattice+ionic geometry that you
obtained, _without_ restarting the electronic structure (ie copying the
new values lattice vectors and ionic coordinates into the input file and
keeping the "restart_mode = 'from_scratch'"): If the lattice constants
start to change a lot, the cut-off energy is too low. Or you look at the
value of the stress at the end of your previous calculation: The final
step is done with re-generated plane waves, so if your lattice changed a
lot and the cut-off was too low, there suddenly is a large value of
stress.
On the other hand I do not know about the accuracy of the pseudo
potential for Ti: I remember there were some problems with a
norm-conserving one, at least if the number of valence electrons is four.
Maybe this one would work better, I do not know this one, but I would
start checking the value of the cut-off energy.
Greetings from Sunny Paris,
apsi
PS Why this "exxdiv_treatment" in your input...?
-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-
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 Tue, 16 Feb 2016, Suresh A wrote:
Dear All,
I have optimized the structure for anatase simple tetragonal. The
optimiized lattice parameters are a= 3.754336A. c=9.193631522694A. but the
experimental values are
a= 3.785A, c=9.514A. There is big difference in c value for optimised
strucutre.But the same calculation for GGA pseudo potential gives the lattice
parameter values which are
good with experimental values. In literature previous results for LDA has
good lattice parameter values.
Which parameter I have to change in order to get good results for LDA?
Below is my input and the version i have used is 5.2.1
&CONTROL
title = 'anatase' ,
calculation = 'vc-relax' ,
restart_mode = 'from_scratch' ,
pseudo_dir = '/home/suresh/GN2/',
outdir ='/home/suresh/Desktop/ashahicheck/asahiopt/tmp/',
prefix = 'anatase' ,
tstress = .true. ,
tprnfor = .true. ,
/
&SYSTEM
ibrav = 6,
A = 3.692,
C = 9.471 ,
nat = 12,
ntyp = 2,
ecutwfc = 60 ,
exxdiv_treatment = 'none' ,
/
&ELECTRONS
/
&IONS
ion_dynamics = 'bfgs' ,
/
&CELL
cell_dynamics = 'bfgs' ,
/
ATOMIC_SPECIES
Ti 47.86700 Ti.pz-mt_fhi.UPF
O 15.99940 O.pz-mt_fhi.UPF
ATOMIC_POSITIONS (crystal)
Ti 0.0000000 0.0000000 0.0000000
Ti 0.5000000 0.0000000 0.7500000
Ti 0.0000000 0.5000000 0.2500000
Ti 0.5000000 0.5000000 0.5000000
O 0.0000000 0.0000000 0.2066000
O 0.5000000 0.0000000 0.5434000
O 0.0000000 0.5000000 0.4566000
O 0.5000000 0.0000000 0.9566000
O 0.0000000 0.5000000 0.0434000
O 0.0000000 0.0000000 0.7934000
O 0.5000000 0.5000000 0.7066000
O 0.5000000 0.5000000 0.2934000
K_POINTS automatic
4 4 2 1 1 1
Thanks in advance.
With Regards,
A.Suresh,
Research Scholar,
Madurai Kamaraj University,
Madurai.
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