<html>
<head>
<meta content="text/html; charset=UTF-8" http-equiv="Content-Type">
</head>
<body bgcolor="#FFFFFF" text="#000000">
<div class="moz-cite-prefix"> Dear Suresh,<br>
<br>
Variable-cell-shape geometry optimization is quite stable in QE
and <br>
free from human errors caused by ignorance or wrong
implementation <br>
of some necessary steps in hand calculations which takes our
valuable time. <br>
Beside in QE you need not worry about symmetry conservation
(unlike SIESTA : <br>
in siesta you should write your own routine to massage
strains). A year ago I was <br>
trying to determine lattice parameters of \alpha-Uranium and
qe's accuracy <br>
was in line between experimental and full-potential values. <br>
<br>
Note that initial guess for lattice paramaters is important but
even for bad <br>
guess (some degree, of course!) their code is smart enough on
choosing <br>
right direction within optimization process.<br>
<br>
Savaş AĞDUK<br>
Research Assistant<br>
Karabuk University<br>
Physics Department<br>
<br>
On 11/06/2013 01:29 PM, Suresh A wrote:<br>
</div>
<blockquote
cite="mid:CAE_UR+WL__v1AgvZ3cXG8HmkWUG=-Xv6gcx8zmCyb0SkaQAKVg@mail.gmail.com"
type="cite">
<div dir="ltr">
<div>
<div>
<div>
<div>
<div>
<div>I am new to QE. I have done variable cell volume
optimization for rutile tio2.<br>
</div>
I confused with finding ground state structure. <br>
<br>
</div>
In literature survey the authors did volume- constraint
total energy minimization and have set cell parameters
a, c and internal parameter( u for rutile)<br>
</div>
finally fitted their value Birch - Murnaghan equation(B-M)
. From the final value they have compared their values
with exprimental values of cell parameter <br>
a,c and elastic parameters.<br>
<br>
</div>
my question is:<br>
<br>
</div>
i) which method is correct whether doing doing vc-relax
alone or collect all volume and total energy from vc-relax
output and fitting this with B-M equation ?<br>
<br>
</div>
ii) How to choose internal parameter u for TiO2 rutile.?<br>
<div>
<div>
<div>
<div>
<div>
<div>i have included the input file. <br>
<br>
&CONTROL<br>
title = 'rutile' ,<br>
calculation = 'vc-relax' ,<br>
restart_mode = 'from_scratch' ,<br>
outdir =
'/home/basheer/Desktop/relax/' ,<br>
pseudo_dir =
'/home/basheer/espresso-5.0.1/pseudo/' ,<br>
prefix = 'rutile' ,<br>
etot_conv_thr = 1.d-6 ,<br>
forc_conv_thr = 1.d-4 ,<br>
tstress = .true. ,<br>
tprnfor = .true. ,<br>
/<br>
&SYSTEM<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 = 200 ,<br>
ecutrho = 800 ,<br>
occupations = 'smearing' ,<br>
degauss = 0.01 ,<br>
smearing = 'gaussian' ,<br>
exxdiv_treatment = 'gygi-baldereschi' ,<br>
/<br>
&ELECTRONS<br>
conv_thr = 1.d-12 ,<br>
/<br>
&IONS<br>
/<br>
&CELL<br>
cell_dynamics = 'bfgs' ,<br>
press_conv_thr = 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>
4 4 4 1 1 1 <br>
<br>
<br clear="all">
</div>
<div>
<div>
<div>
<div>
<div dir="ltr">
<div>
<div>
<div>
<div
style="margin-left:40px;text-align:right">
<br>
</div>
<div style="text-align:right">A.Suresh,<br>
</div>
</div>
<div style="text-align:right">Project
Fellow,<br>
</div>
</div>
<div style="text-align:right">Madurai
Kamaraj University,<br>
</div>
</div>
<div style="text-align:right">
Madurai.<br>
</div>
</div>
</div>
</div>
</div>
</div>
</div>
</div>
</div>
</div>
</div>
</div>
<br>
<fieldset class="mimeAttachmentHeader"></fieldset>
<br>
<pre wrap="">_______________________________________________
Pw_forum mailing list
<a class="moz-txt-link-abbreviated" href="mailto:Pw_forum@pwscf.org">Pw_forum@pwscf.org</a>
<a class="moz-txt-link-freetext" href="http://pwscf.org/mailman/listinfo/pw_forum">http://pwscf.org/mailman/listinfo/pw_forum</a></pre>
</blockquote>
<br>
</body>
</html>