[Pw_forum] calculating cohesive energy

[udayagiri sai babu]

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)*

*input 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      0.00000000
K_POINTS {automatic}
8 8 8 0 0 0
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