[Pw_forum] Lattice constant for copper

[Eric Germaneau]

Hey,

I'm a newbie too and I'm wondering how can you equilibrate the lattice 
constant by doing just a scf calculation.
Also, it seems to me that only MD is able to reproduce experimental data 
since it takes into account the temperature and the pressure.
Please, let me know if I'm wrong.

                     Eric.

On 03/02/2011 05:58 PM, Krukau, Aliaksandr wrote:
>     Dear QE users,
>      I apologize if my question seems stupid to you. I am a complete QE newbie
> and could not find any answer in the tutorials.
>      I am trying to find equilibrium lattice constant for copper with PBE
> and ultrasoft pseudopotentials. I ran scf calculations for face-centered cubic
> unit cell for a number of lattice constants:
> Lattice constant 6.65 a.u. !    total energy              =
> -121.62734203 Ry
> Lattice constant 6.66 a.u. !    total energy              =
> -121.62735421 Ry
> Lattice constant 6.67 a.u. !    total energy              =
> -121.62734651 Ry
> Lattice constant 6.65 a.u. !    total energy              =
> -121.62731956 Ry
>      The minimum total energy is for the lattice constant 6.66 a.u.
> But this value drastically differs from the published PBE value of 6.86 a.u.
> (Phys. Rev. B, vol. 77, 05414 (2008), Table II). It also differs from
> the experimental value of 6.83 a.u. I attach the input file that I used
> for lattice constant 6.66 a.u. below the signature.
>      Why is equilibrium lattice constant so low?
> Best regards,
> Alex Krukau,
> Indiana University
>
> ------------------------------------------------------
> &control
>      calculation='scf'
>      pseudo_dir = '~/espresso-4.2.1/pseudo/ADDITIONAL',
> /
> &system
>      ibrav = 2,
>      celldm(1) = 6.66,
>      nat= 1,
>      ntyp= 1,
>      ecutwfc = 120.0,
>      ecutrho = 1000.0
>      occupations='smearing', smearing='marzari-vanderbilt', degauss=0.01
> /
> &electrons
>      conv_thr=0.0000001
> /
> ATOMIC_SPECIES
> Cu  63.546 Cu.pbe-n-van_ak.UPF
> ATOMIC_POSITIONS
> Cu 0.0 0.0 0.0    1   1   1
> K_POINTS automatic
> 12 12 1 0 0 0
>
>
>
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-- 
/Be the change you wish to see in the world
/ --- Mahatma Gandhi ---

Dr. Éric Germaneau <mailto:germaneau at gucas.ac.cn>

College of Physical Sciences
Graduate University of Chinese Academy of Sciences
Yuquan Road 19A
Beijing 100049
China

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