[Pw_forum] Lattice constant for copper

[Duy Le]

Did you check your k-point sampling?
--------------------------------------------------
Duy Le
PhD Student
Department of Physics
University of Central Florida.

"Men don't need hand to do things"



On Wed, Mar 2, 2011 at 5:58 PM, Krukau,  Aliaksandr <akrukau at indiana.edu> 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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