[Pw_forum] Cr GGA potential is underestimating the cohesive energy.

[udayagiri sai babu]

Dear all
I am calculated the cohesive energy of Cr using the pseudopotential
Cr.pbe-sp-van.UPF. I got is *3.63* *ev/atom* as the cohesive energy where as
the experimental value is *4.1 ev/atom*. As i know the GGA pseudopotential
should overestimate the cohesive energy value but here it is
underestimating. What is the problem? can somebody please help me out.
The magnetic state of the Cr in the bulk is antiferromagnetic at zero kelvin
(Neel temperature is ~312 K). For the sake of complete information below are
my input files.

*Bulk*
&control
calculation = 'scf',
restart_mode='from_scratch',
outdir='/home/sai/softwares/espresso-4.0.1/workspace/cr_paramagnetic/temp',
prefix='chromium'
pseudo_dir='/home/sai/softwares/espresso-4.0.1/pseudo/',
/
&system
ibrav=1
celldm(1)=5.250000,
nat=2,
ntyp=2,
ecutwfc=60,
ecutrho=600,
occupations='smearing',
smearing='mp',
degauss=0.010000
nspin=2
starting_magnetization(1)=0.5
starting_magnetization(2)=-0.5
/
&electrons
conv_thr=1.D-8,
diagonalization='david',
mixing_mode='plain',
mixing_beta= 0.7
/
ATOMIC_SPECIES
Cr1  51.9961  Cr.pbe-sp-van.UPF
Cr2  51.9961  Cr.pbe-sp-van.UPF
ATOMIC_POSITIONS (crystal)
Cr1 0.00 0.00 0.00
Cr2 0.5 0.5 0.5
K_POINTS {automatic}
10 10 10 0 0 0

*Isolated*
&control
calculation = 'scf',
restart_mode='from_scratch',
outdir='/home/sai/softwares/espresso-4.0.1/workspace/cr_paramagnetic/temp',
prefix='chromium'
pseudo_dir='/home/sai/softwares/espresso-4.0.1/pseudo/',
/
&system
ibrav=1
celldm(1)=15,
nat=1,
ntyp=1,
ecutwfc=60,
ecutrho=600,
occupations='fixed',
tot_magnetization=6
nspin=2
nosym=.true.,
/
&electrons
conv_thr=1.D-8,
diagonalization='david',
mixing_mode='plain',
mixing_beta= 0.7
/
ATOMIC_SPECIES
Cr  51.9961  Cr.pbe-sp-van.UPF
ATOMIC_POSITIONS (crystal)
Cr 0.00 0.00 0.00
K_POINTS {automatic}
1 1 1 0 0 0
-- 
U.Saibabu
PhD student,
Deformation mechanisms modeling group,
Materials engineering department,
IISc Bangalore,
India.
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