[Pw_forum] DC & BEC

[Nicola Marzari]

Dear Suza,


slightly puzzling - one thing I recall is that these perovskites
can reach an incorrect ground state where some of the higher
occupied eigenstates have converged to even higher unoccupied
states (this is in principle possible with some of the iterative
algorithms used e.g. in PWSCF or VASP).

This is typically cured by using startignwfc="atomic+random" -
it looks like this has now become the default in pwscf, but depending on
the version you use it might not have been the case.

LEt us know,

			nicola



On 11/30/11 10:32 PM, Suza W wrote:
>
> Dear All,
>
> Being an epitome of ferroelectric, BaTiO3 has extensively been
> studied using PWSCF. However, unfortunately, with several
> standard available USPP, I encounter following unphysical results :
>
> Dielectric constant in cartesian axis
>
> (-8142842.391767483 0.000000000 0.000000000 )
> ( 0.000000000-8142842.391767481 0.000000000 )
> ( 0.000000000 0.000000000-8142842.391767476 )
>
> Effective charges (d Force / dE) in cartesian axis
>
> atom 1 Ba
> Ex ( -1136.43937 0.00000 0.00000 )
> Ey ( 0.00000 -1136.43937 0.00000 )
> Ez ( 0.00000 0.00000 -1136.43937 )
> atom 2 Ti
> Ex ( -1874.03151 0.00000 0.00000 )
> Ey ( 0.00000 -1874.03151 0.00000 )
> Ez ( 0.00000 0.00000 -1874.03151 )
> atom 3 O
> Ex ( 931.42284 0.00000 0.00000 )
> Ey ( 0.00000 1067.39482 0.00000 )
> Ez ( 0.00000 0.00000 1067.39482 )
> atom 4 O
> Ex ( 1067.39482 0.00000 0.00000 )
> Ey ( 0.00000 931.42284 0.00000 )
> Ez ( 0.00000 0.00000 1067.39482 )
> atom 5 O
> Ex ( 1067.39482 0.00000 0.00000 )
> Ey ( 0.00000 1067.39482 0.00000 )
> Ez ( 0.00000 0.00000 931.42284 )
>
> Any suggestion for correcting these errors will be highly appreciated.
> Here goes the input file which renders such a blunder.
> &system
> ibrav = 1,
> celldm(1) = 7.5589,
> nat = 5,
> ntyp=3,
> ecutwfc = 30.0,
> ecutrho = 240.0,
> /
> &electrons
> diagonalization = 'david'
> conv_thr = 1.0d-9
> mixing_beta = 0.7
> /
> &ions
> /
> &cell
> /
> ATOMIC_SPECIES
> Ba 137.327 Ba.pbe-nsp-van.UPF
> Ti 47.867 Ti.pbe-sp-van_ak.UPF
> O 15.9994 O.pbe-van_ak.UPF
> ATOMIC_POSITIONS (alat)
> Ba 0.0 0.0 0.0
> Ti 0.5 0.5 0.5
> O 0.0 0.5 0.5
> O 0.5 0.0 0.5
> O 0.5 0.5 0.0
> K_POINTS {automatic}
> 8 8 8 1 1 1
>
> Thanking you,
> Yours sincerely,
> Suza W
> PhD Student
> Department of Materials Science
> Bangalore
>
>
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-- 

----------------------------------------------------------------------
Prof Nicola Marzari, Chair of Theory and Simulation of Materials, EPFL