[QE-users] nscf in super cell

[Paolo Giannozzi]

On Tue, May 12, 2020 at 7:08 AM Fariba Islam <ezqhaz at gmail.com> wrote:

> I wrote the following code for nscf calculation of a silicon supercell.
> Why do I get
>
"c_bands:  2 eigenvalues not converged
>  c_bands:  1 eigenvalues not converged...." in my output file and the
> calculation is not stopping
>

if it is not stopping, there is no problem. In a scf calculation, the
iterative diagonalization starts from wavefunctions computed at the
previous scf step and usually converges quickly. The maximum number of
internal iterations is thus small (20 if I remember correctly). In a
non-scf calculation, there isn't such a good starting point and iterative
diagonalization sometimes does not converge for all eigenvalues in 20
iterations, but it is usually sufficient to repeat the diagonalization.

Paolo

&control
>     calculation = 'nscf'
>     restart_mode='from_scratch'
>     prefix = 'si_b'
>     outdir='./tmp/'
>     pseudo_dir='../pseudo/'
> /
> &system
>     ibrav=2, celldm(1) = 20.8218,
>     nat=16, ntyp=1,
>     ecutwfc=40
>     ecutrho=160
>     noinv=.true.
>     nosym=.true.
>     occupations='smearing' , smearing='gaussian',degauss=0.005
> /
> &electrons
>     conv_thr=1e-8
> /
> ATOMIC_SPECIES
>  Si  28.0855  Si_ONCV_PBE-1.0.upf
>
> ATOMIC_POSITIONS (alat)
> Si 0.000000   0.000000   0.000000
> Si -0.374989   0.375011   0.375011
> Si -0.250000   0.250000   0.000000
> Si -0.624989   0.625011   0.375011
> Si 0.000000   0.250000   0.250000
> Si -0.374989   0.625011   0.625011
> Si -0.250000   0.500000   0.250000
> Si -0.624989   0.875011   0.625011
> Si -0.250000   0.000000   0.250000
> Si -0.624989   0.375011   0.625011
> Si -0.500000   0.250000   0.250000
> Si -0.874989   0.625011   0.625011
> Si -0.250000   0.250000   0.500000
> Si -0.624989   0.625011   0.875011
> Si -0.500000   0.500000   0.500000
> Si -0.874989   0.875011   0.875011
>
> K_POINTS {automatic}
> 12 12 12 0 0 0
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-- 
Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222
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