[Pw_forum] calculating cohesive energy

[Stefano Baroni]

No need to post twice the same message ...
Don't now about your specific system, but it is not unusual that DFT  
overestimate binding energies (less so for PBE than LDA)
Please, do not forget to sign your posts, including your affiliation
SB

On Aug 31, 2009, at 8:37 PM, udayagiri sai babu wrote:

> 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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---
Stefano Baroni - SISSA  &  DEMOCRITOS National Simulation Center -  
Trieste
http://stefano.baroni.me [+39] 040 3787 406 (tel) -528 (fax) /  
stefanobaroni (skype)

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