[Pw_forum] vc-relax gives good result of lattice constant, but not good in cohesive energy

[mohnish pandey]

You have to do the spin-polarized calculation for isolated atom. Zr has two
unpaired electron in outer d-shell.


On Tue, Jun 4, 2013 at 1:02 PM, Dongsheng Zhang <zhdsheng21 at gmail.com>wrote:

> Hi,
>
> I am calculating the optimum lattice constant nd cohesive energy of Zr hcp
> crystal. The total energy of a sinle Zr atom I got from input file Zr.in is
> -5.53133015 Ry, the total energy of Zr hcp crystal I got from input file
> Zr.hcp.in is -12.13562915 Ry, so the cohesive energy is -0.536 Ry,
> converted to -7.30 eV. From a reference paper, the cohesive energy should
> be -6.2eV. Attached below are Zr.in and Zr.hcp.in. Could anyone tell me
> if I had made any mistake in those input files? Thanks.
>
> Zr.in:
>
> &control
>     prefix='Zr',
>     pseudo_dir = '/home/zhang/Software/espresso_PP/',
>     outdir='/share/scratch/tmpZr/eCut120SM0.01/',
>  /
>  &system
>     ibrav=  1, celldm(1) =50, nat=  1, ntyp= 1,
>     occupations='smearing', smearing='marzari-vanderbilt', degauss=0.01,
>     ecutwfc =120,
>
>  /
>  &electrons
>  /
> ATOMIC_SPECIES
>  Zr  91.224 Zr.pbe-mt_fhi.UPF
> ATOMIC_POSITIONS
>   Zr  0.000000000000 0.000000000000 0.000000000000
> K_POINTS gamma
>
>
> Zr.hcp.in
>
> &control
>     prefix='Zr',
>     pseudo_dir = '/home/zhang/Software/espresso_PP/',
>     outdir='/share/scratch/tmpZr/eCut120K18hcpSM0.01/',
>     calculation='vc-relax'
>  /
>  &system
>     ibrav=  4, celldm(1) =6, celldm(3) =1.633, nat=  2, ntyp= 1,
>     occupations='smearing', smearing='marzari-vanderbilt', degauss=0.01,
>     ecutwfc =120,
>  /
>  &electrons
>  /
>  &ions
>  /
>  &cell
>  /
> ATOMIC_SPECIES
>  Zr  91.224 Zr.pbe-mt_fhi.UPF
> ATOMIC_POSITIONS crystal
>   Zr  0.000000000000 0.000000000000 0.000000000000
>   Zr  0.666666666666 0.333333333333 0.50000000000
> K_POINTS automatic
> 18 18 36 1 1 1
>
> PS The optimum lattice constant got from Zr.hcp.in is very close to the
> data in literature.
>
>
> I have tried different value of the smearing parameter ranged from 0.001
> to 0.05, none of their cohesive energy is good.
>
> If the smearing value is 0.1, simulation by zr.in (single atom) will stop
> at iteration # 10 without any error message. Why does it happen?
>
> Thank you for your help,
>
> Dongsheng
>
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>



-- 
Regards,
MOHNISH,
-----------------------------------------------------------------
Mohnish Pandey,
PhD Student,
Center for Atomic-scale Materials Design,
Department of Physics,
Technical University of Denmark
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