<div dir="ltr"><div style="text-align:left"><div dir="ltr"><div><div><div><div>I have done vc-relax calculation on rutile to find out ground<br>
state structure of the system. While looking at my input and output file<br>
1)SAVA told that "symmetry is broken and suggested to solve cutoff related<br>
issues"<br>
2)EMINE told that if high ecutoff values needed for stress tensor<br>
convergence than better go for equation of state than vc-relax,<br>
3) Giuseppe suggested something on exxdiv_treatment and questioned reason<br>
for high ecutoff value 200/800.<br>
Now i have repeated my calculation the input file is included here<br>
&CONTROL<br>
title = 'rutile' ,<br>
calculation = 'vc-relax' ,<br>
restart_mode = 'from_scratch' ,<br>
outdir = '/home/basheer/Desktop/relax2/<div id=":pf">' ,<br>
pseudo_dir =<br>
'/home/basheer/Desktop/espresso-5.0.1/pseudo/' ,<br>
disk_io = 'high' ,<br>
verbosity = 'high' ,<br>
etot_conv_thr = 1.d-8 ,<br>
forc_conv_thr = 1.d-4 ,<br>
tstress = .true. ,<br>
tprnfor = .true. ,<br>
/<br>
&SYSTEM<br>
<br>
- Ignored:<br>
ibrav = 6,<br>
A = 4.59373 ,<br>
B = 4.59373 ,<br>
C = 2.95812 ,<br>
cosAB = 0 ,<br>
cosAC = 0 ,<br>
cosBC = 0 ,<br>
nat = 6,<br>
ntyp = 2,<br>
ecutwfc = 50 ,<br>
ecutrho = 200 ,<br>
nosym = .true. ,<br>
exxdiv_treatment = 'none' ,<br>
/<br>
&ELECTRONS<br>
conv_thr = 1.d-12 ,<br>
/<br>
&IONS<br>
/<br>
&CELL<br>
cell_dynamics = 'bfgs' ,<br>
cell_factor = 2 ,<br>
/<br>
ATOMIC_SPECIES<br>
Ti 47.88800 Ti.pz-mt_fhi.UPF<br>
O 15.99900 O.pz-mt_fhi.UPF<br>
ATOMIC_POSITIONS angstrom<br>
Ti 0.000000000 0.000000000 0.000000000<br>
Ti 2.296860000 2.296860000 1.479060000<br>
O 1.402470000 1.402470000 0.000000000<br>
O 3.191260000 3.191260000 0.000000000<br>
O 0.894400000 3.699330000 1.479060000<br>
O 3.699330000 0.894400000 1.479060000<br>
K_POINTS automatic<br>
6 6 6 0 0 0<br>
<br>
for this input the output is<br>
Begin final coordinates<br>
new unit-cell volume = 365.14180 a.u.^3 ( 54.10843 Ang^3 )<br>
<br>
CELL_PARAMETERS (alat= 8.68089163)<br>
0.950810397 0.000000544 0.000000000<br>
0.000000544 0.950810397 0.000000000<br>
0.000000000 0.000000000 0.617420010<br>
entering subroutine stress ...<br>
<br>
total stress (Ry/bohr**3) (kbar) P=<br>
0.13<br>
0.00000085 -0.00000001 -0.00000000 0.12 -0.00 -0.00<br>
-0.00000001 0.00000085 -0.00000000 -0.00 0.12 -0.00<br>
-0.00000000 -0.00000000 0.00000104 -0.00 -0.00 0.15<br>
entering subroutine stress ...<br>
<br>
total stress (Ry/bohr**3) (kbar) P=<br>
-236.66<br>
-0.00164796 -0.00000002 -0.00000000 -242.42 -0.00 -0.00<br>
-0.00000002 -0.00164796 -0.00000000 -0.00 -242.42 -0.00<br>
-0.00000000 -0.00000000 -0.00153033 -0.<span tabindex="0" class=""><span class="">00</span></span> -0.00 -225.12<br>
the output shows lattice parameter is 95% what i have<br>
given in input and also stress tensor is not converged. When i checked the<br>
output structure it shows 2 apical bonds(2 Ti-O BONDS) are lower than other<br>
four equitorial bonds(4 Ti-O BONDS) but experimental shows two apical bond<br>
should be higher than four equitorial bonds. But when i increase gradually<br>
ecutoff value 50 to 100 by step by step the output lattice parameter is 98%<br>
of what i have given initially and stress tensor also converged as below.<br>
and 2 apical bonds(2 Ti-O BONDS) are higher than other four equitorial<br>
bonds(4 Ti-O BONDS) as experimental value shows.<br>
<br>
Begin final coordinates<br>
new unit-cell volume = 400.44101 a.u.^3 ( 59.33924 Ang^3 )<br>
<br>
CELL_PARAMETERS (alat= 8.68089163)<br>
0.983405137 0.000000000 0.000000000<br>
0.000000000 0.983405137 0.000000000<br>
0.000000000 0.000000000 0.632966319<br>
entering subroutine stress ...<br>
<br>
total stress (Ry/bohr**3) (kbar) P=<br>
0.01<br>
0.00000006 0.00000000 0.00000000 0.01 0.00 0.00<br>
0.00000000 0.00000006 0.00000000 0.00 0.01 0.00<br>
0.00000000 0.00000000 0.00000005 0.00 0.00 0.01<br>
<br>
total stress (Ry/bohr**3) (kbar) P=<br>
0.18<br>
0.00000123 0.00000000 0.00000000 0.18 0.00 0.00<br>
0.00000000 0.00000123 0.00000000 0.00 0.18 0.00<br>
0.00000000 0.00000000 0.00000121 0.00 0.00 0.18<br>
in this calculation i remove exx_divtreatment, and occupations=smearing<br>
cards. is this calculation is correct or i have to go for equation state?<br>
and whether symmetry is preserved for ecut=100? Which one i have to choose<br>
ecut =50 or 100 because for 100 only i got 98% lattice parameter than my<br>
input latticeparameter value. while i doing energy convergence test energy<br>
is converged at ecut=50, what about this?<br><div>
Thank You</div></div>A.Suresh,<br></div></div><div>Project Fellow,<br></div></div><div>Madurai Kamaraj University,<br></div></div><div>Madurai.<br></div></div></div>
</div>