Thanks guys ,i got the cohesive energy by including the spin in my input file. <br><br><div class="gmail_quote">On Tue, Sep 1, 2009 at 10:10 AM, <span dir="ltr"><<a href="mailto:elbuesta@icqmail.com">elbuesta@icqmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"><div class="im">I calculated some time ago some bulk properties of Vanadium using the<br>
same PP you used and I obtained the following:<br>
<br>
Isolated: -27.260Ry<br>
Bulk: -27.666Ry (a=5.675)<br>
Cohesive energy: 5.52eV/atom<br>
Predicted equilibrium lat. param.: 3.00angstrom (Experimental is 3.03,<br>
I think)<br>
<br>
The equilibrium values are well reproduced.<br>
I don't remember (I don't have the inputs with me) exactly all the<br>
details, but the difference is probably related to the fact that spin<br>
has to be included for the isolated atom, as already mentioned by other<br>
PW users.<br>
<br>
All best.<br>
<br>
</div>P.S: Sorry for sending two e-mails.<br>
<div><div></div><div class="h5"><br>
Fábio Negreiros Ribeiro<br>
PHd student - Departamento de Física - Universidade Federal de Minas<br>
Gerais<br>
Belo Horizonte - MG - Brazil<br>
<br>
-----Original Message-----<br>
From: udayagiri sai babu <<a href="mailto:udayagiri3@gmail.com">udayagiri3@gmail.com</a>><br>
To: <a href="mailto:pw_forum@pwscf.org">pw_forum@pwscf.org</a><br>
Sent: Mon, Aug 31, 2009 8:37 pm<br>
Subject: [Pw_forum] calculating cohesive energy<br>
<br>
Hi all<br>
i am claculating cohesive energy of V using pwscf but i got<br>
-8.15 ev/atom against an experimental value of 5.3 ev/atom which is<br>
almost 50% off can anybody say what is going wrong with the<br>
calculation. the method i used is calculate the total energy of a bcc<br>
crystal with 1 atom and deduct the energy of isolated atom from it. the<br>
following input files are for finding the total energy for isolated<br>
atom and the atom in the crystal. Please tell me if my methodology is<br>
wrong.<br>
<br>
<br>
cohesive energy=E per atom (in the crystal)-E<br>
per atom (isolated)<br>
<br>
inpu<br>
t file for finding the total energy of an isolated atom<br>
<br>
&control<br>
calculation = 'scf',<br>
restart_mode='from_scratch',<br>
<br>
<br>
outdir='/home/sai/temp',<br>
prefix='vanadium'<br>
pseudo_dir='/home/sai/softwares/espresso-4.0.1/pseudo/',<br>
tstress = .TRUE.,<br>
tprnfor = .TRUE.,<br>
/<br>
&system<br>
<br>
ibrav=1<br>
celldm(1)=30,<br>
<br>
nat=1,<br>
ntyp=1<br>
ecutwfc=25,<br>
ecutrho=100,<br>
occupations='smearing',<br>
smearing='mv',<br>
degauss=0.010000<br>
/<br>
&electrons<br>
conv_thr=1.D-8,<br>
diagonalization='david',<br>
mixing_mode='plain',<br>
<br>
<br>
mixing_beta= 0.3<br>
/<br>
ATOMIC_SPECIES<br>
V 50.9415 V.pbe-n-van.UPF<br>
ATOMIC_POSITIONS (crystal)<br>
V 0.00000000 0.00000000 0.00000000<br>
K_POINTS {automatic}<br>
1 1 1 0 0 0<br>
<br>
input file for finding the total energy of the atom in the crystal<br>
<br>
<br>
<br>
&control<br>
calculation = 'scf',<br>
restart_mode='from_scratch',<br>
outdir='/home/sai/temp',<br>
prefix='vanadium'<br>
pseudo_dir='/home/sai/softwares/espresso-4.0.1/pseudo/',<br>
<br>
<br>
tstress = .TRUE.,<br>
tprnfor = .TRUE.,<br>
/<br>
&system<br>
ibrav=3<br>
celldm(1)=5.654,<br>
nat=1,<br>
ntyp=1<br>
ecutwfc=25,<br>
ecutrho=100,<br>
occupations='smearing',<br>
smearing='mv',<br>
degauss=0.010000<br>
<br>
<br>
/<br>
&electrons<br>
conv_thr=1.D-8,<br>
diagonalization='david',<br>
mixing_mode='plain',<br>
mixing_beta= 0.3<br>
/<br>
ATOMIC_SPECIES<br>
V 50.9415 V.pbe-n-van.UPF<br>
ATOMIC_POSITIONS (crystal)<br>
</div></div>V 0.00000000 0.00000000 200.00000000<br>
<div><div></div><div class="h5"><br>
<br>
K_POINTS {aut<br>
omatic}<br>
8 8 8 0 0 0_______________________________________________<br>
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</div></div></blockquote></div><br><br clear="all"><br>-- <br>U.Saibabu<br>PhD student,<br>Deformation mechanisms modeling group,<br>Materials engineering department,<br>IISc Bangalore,<br>India.<br><br>