[Pw_forum] cohesive energy

[William Parker]

Hi Udayaghiri,

Please indicate your affiliation (and preferred name).

My suggestions are:

1) Converge the k-point mesh better for the solid.  V is a metal and
probably needs more than 8x8x8.

2) Check the energy cutoff convergence on the pseudo-atom.  I find that I
need more plane waves to describe it than the solid for a given
pseudopotential.

--William

======================================================================
William Parker              Tel :  +1 (614) 292-2887
Graduate Research Associate Fax :  +1 (614) 292-7557
Ohio State University
Department of Physics
191 West Woodruff Avenue    email: wparker at mps.ohio-state.edu
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U.S.A.

Office: 2025 Physics Research Building
======================================================================

On Mon, 31 Aug 2009, 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
>