[Pw_forum] calculating cohesive energy

[udayagiri sai babu]

Thanks guys ,i got the cohesive energy by including the spin in my input
file.

On Tue, Sep 1, 2009 at 10:10 AM, <elbuesta at icqmail.com> wrote:

> 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_______________________________________________
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>
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-- 
U.Saibabu
PhD student,
Deformation mechanisms modeling group,
Materials engineering department,
IISc Bangalore,
India.
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