Dear Xufeng,
from a first view your results seem reliable.
Indeed you are right that for an isolated, k-isotropic band one would expect a
sqrt(E) behaviour of the DOS near the band bottom (for perfect sampling and
integration :D). I think if you are not to harsh with yourself, you can see
this in your calculations for the first 80meV.
Have in mind that depending on your calculation (LDA/GGA, strained etc..) a
band folds in around 100-150meV above the CBM and changes the
sqrt(E)-behaviour.
Second the „effective mass“ is strictly speaking k-dependent as 1/m \propto
del^2 E_{k} / del k^2 \propto del/del k v_{k}, as you can see in fig 3
https://img2.picload.org/image/rowwrwir/1.png
<https://img2.picload.org/image/rowwrwir/1.png>
where v_k is shown 100meV above the CBM. I used only a coarse mesh of ~4000k,
but get similar results as you. Ignoring the oscillations, the dependence of
DOS^2 is almost linear, too.
So again, it depending on what you want to calculate afterwards, your results
look pretty okay.
bests,
Nicki
DTU Denmark, CAMd
> Am 18.02.2017 um 12:00 schrieb [email protected]:
>
> Message: 3
> Date: Fri, 17 Feb 2017 21:05:59 -0500
> From: Xufeng Wang <[email protected] <mailto:[email protected]>>
> Subject: [Pw_forum] Silicon DOS issue
> To: [email protected] <mailto:[email protected]>
> Message-ID:
> <cah5zo9+vg-7tfvrm2hc+6n_ajtzbu7dxpfhythuim_bobap...@mail.gmail.com
> <mailto:cah5zo9+vg-7tfvrm2hc+6n_ajtzbu7dxpfhythuim_bobap...@mail.gmail.com>>
> Content-Type: text/plain; charset="utf-8"
>
> Dear community,
>
> I am unable to obtain the square root energy dependency of the bulk Silicon
> conduction band DOS, despite using a fine k grid (100x100x100).
>
> I expect the DOS near conduction band edge (below the second conduction
> band of silicon) has a square root dependence with energy. I plotted out
> the (DOS)^2 vs energy I obtained here: http://imgur.com/a/Wu07z
> <http://imgur.com/a/Wu07z>
>
> As you can see, (DOS)^2 vs. energy is not linear, meaning DOS is not having
> a square root dependence with energy. Is this an known problem or am I
> doing something wrong? Here is the nscf calculation input deck:
>
> -------
>
> &control
>
> prefix='silicon',
>
> pseudo_dir='../pseudo/'
>
> outdir = './results',
>
> tstress=.false.,
>
> tprnfor=.false.,
>
> calculation = 'nscf',
>
> verbosity='high',
>
> /
>
> &system
>
> ibrav= 2, celldm(1) =10.2623466921, nat= 2, ntyp= 1,
>
> ecutwfc = 30.0, ecutrho=300.0, input_dft='PBE', nbnd = 8,
>
> /
>
> &electrons
>
> diagonalization = 'david',
>
> conv_thr = 1d-08,
>
> mixing_mode = 'plain',
>
> mixing_beta = 0.7,
>
> /
>
> ATOMIC_SPECIES
>
> Si 28.086 Si.pbe-n-rrkjus_psl.0.1.UPF
>
> ATOMIC_POSITIONS
>
> Si 0.00 0.00 0.00
>
> Si 0.25 0.25 0.25
>
> K_POINTS automatic
>
> 100 100 100 0 0 0
> -------
>
> Thanks!
>
> Xufeng
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