[Pw_forum] calculating cohesive energy

[elbuesta at icqmail.com]

I calculated some time ago some bulk properties of Vanadium using the
same PP you used and I obtained the following:

Isolated: -27.260Ry
Bulk: -27.666Ry (a=5.675)
Cohesive energy: 5.52eV/atom
Predicted equilibrium lat. param.: 3.00angstrom (Experimental is 3.03,
I think)

The equilibrium values are well reproduced.
I don't remember (I don't have the inputs with me) exactly all the
details, but the difference is probably related to the fact that spin
has to be included for the isolated atom, as already mentioned by other
PW users.

All best.

P.S: Sorry for sending two e-mails.

Fábio Negreiros Ribeiro
PHd student - Departamento de Física - Universidade Federal de Minas
Gerais
Belo Horizonte - MG - Brazil

-----Original Message-----
From: udayagiri sai babu <udayagiri3 at gmail.com>
To: pw_forum at pwscf.org
Sent: Mon, Aug 31, 2009 8:37 pm
Subject: [Pw_forum] calculating cohesive energy

Hi all
i am claculating cohesive energy of V using pwscf but i got
-8.15 ev/atom against an experimental value of 5.3 ev/atom which is
almost 50% off can anybody say what is going wrong with the
calculation. the method i used is calculate the total energy of a bcc
crystal with 1 atom and deduct the energy of isolated atom from it. the
following input files are for finding the total energy for isolated
atom and the atom in the crystal. Please tell me if my methodology is
wrong.


cohesive energy=E per atom (in the crystal)-E 
per atom (isolated)

inpu
t file for finding the total energy of an isolated atom

&control
calculation = 'scf',
restart_mode='from_scratch',


outdir='/home/sai/temp',
prefix='vanadium'
pseudo_dir='/home/sai/softwares/espresso-4.0.1/pseudo/',
tstress = .TRUE.,
tprnfor = .TRUE.,
/
&system

ibrav=1
celldm(1)=30,

nat=1,
ntyp=1
ecutwfc=25,
ecutrho=100,
occupations='smearing',
smearing='mv',
degauss=0.010000
/
&electrons
conv_thr=1.D-8,
diagonalization='david',
  mixing_mode='plain',


mixing_beta= 0.3
/
ATOMIC_SPECIES
V  50.9415  V.pbe-n-van.UPF
ATOMIC_POSITIONS (crystal)
V       0.00000000      0.00000000      0.00000000
K_POINTS {automatic}
1 1 1 0 0 0

input file for finding the total energy of the atom in the crystal



&control
calculation = 'scf',
restart_mode='from_scratch',
outdir='/home/sai/temp',
prefix='vanadium'
pseudo_dir='/home/sai/softwares/espresso-4.0.1/pseudo/',


tstress = .TRUE.,
tprnfor = .TRUE.,
/
&system
ibrav=3
celldm(1)=5.654,
nat=1,
ntyp=1
ecutwfc=25,
ecutrho=100,
occupations='smearing',
smearing='mv',
degauss=0.010000


/
&electrons
conv_thr=1.D-8,
diagonalization='david',
mixing_mode='plain',
mixing_beta= 0.3
/
ATOMIC_SPECIES
V  50.9415  V.pbe-n-van.UPF
ATOMIC_POSITIONS (crystal)
V       0.00000000      0.00000000     200.00000000


K_POINTS {aut
omatic}
8 8 8 0 0 0_______________________________________________
Pw_forum mailing list
Pw_forum at pwscf.org
http://www.democritos.it/mailman/listinfo/pw_forum