[Pw_forum] Problem with PDOS of ionic crystals

[Giovanni Cantele]

On 04 Apr 2014, at 10:43, Alexander G. Kvashnin <agkvashnin at gmail.com> wrote:

> Dear QE users,
> 
> I tried to calculate PDOS for simple cubic NaCl structure. I performed an optimization vc-relax with 6x6x6 k-points, than I made scf calculations, nscf calculations and after that I ran projwfc to plot PDOS. 
> My question is why when I plotted DOS_Na+DOS_Cl it differs from the total DOS for whole system, specially in conduction band?
> 
> Here is my nscf file and input file for projfwc:
> 
>  &control
>     calculation='nscf'
>     restart_mode='restart',
>     tstress = .true.
>     tprnfor = .true.
>     prefix='nacl',
>     pseudo_dir = '.',
>     outdir='.',
>     nstep = 200 
>  /
>  &system
>                     nosym = .false.,
>                      ibrav = 1,
>                      nat = 4,
>                      ntyp = 2,
>                      ecutwfc = 30,
>                      celldm(1) = 10.750047341391399,
>                      occupations = 'tetrahedra',
>  /
>  &electrons
>     conv_thr =  1.0d-8
>     mixing_beta = 0.7
>     electron_maxstep = 300
>  /
> ATOMIC_SPECIES
>  Na    22.9897    Na.pbe-sp-van_ak.UPF
>  Cl    35.4527    Cl.pbe-n-van.UPF
> ATOMIC_POSITIONS  crystal
> Na      -0.500000000  -0.500000000   0.000000000
> Na      -0.500000000   0.000000000  -0.500000000
> Cl      -0.500000000   0.000000000   0.000000000
> Cl      -0.500000000  -0.500000000  -0.500000000
> Cl       0.000000000  -0.500000000   0.000000000
> Cl       0.000000000   0.000000000  -0.500000000
> Na       0.000000000   0.000000000   0.000000000
> Na       0.000000000  -0.500000000  -0.500000000
> K_POINTS automatic 
>  6 6 6  0 0 0
> 
>  &inputpp
>     outdir='./'
>     prefix='nacl'
>     ngauss=1, degauss=0.02
>     DeltaE=0.05
>     Emin=-15.0, Emax=15.0,
>     filpdos='nacl.k'
>  /
> 
> 
> Any suggestion are welcome!
> Thank you in advance!
>  --
> Sincerely yours,
> Alexander G. Kvashnin 
> =====================================================
> PhD Student 
> Moscow Institute of Physics and Technology          http://mipt.ru/
> 141700, Institutsky lane 9, Dolgoprudny, Moscow Region, Russia
> 
> Junior research scientist
> Technological Institute for Superhard 
> and Novel Carbon Materials                                http://www.tisnum.ru/
> 142190, Central'naya St. 7a, Troitsk, Moscow Region, Russia
> =====================================================	
> 



Dear Alexander,

inside the pdos output file you should find, for EACH eigenvalue at EACH k-point the decomposition of
the wave function, together with the sum of the square modulus of the expansion coefficients.

What you should notice is that, while for occupied states |psi|^2 = 1.000, the coefficient square moduli do
not sum up to 1, as you move to high energy unoccupied states.

Should the basis set used for the projection be orthogonal and complete, that should not occur. However,
the code, as far as I remember, is only able to project onto the atomic orbitals included in the pseudo potentials.

Therefore, while the bands, even though unoccupied, are correctly (at DFT level!) computed, the projection onto
the atomic orbitals might not be enough because would require atomic orbitals (e.g. d states) not included
in the pseudo. The result is that the sum of the partial dos is LESS than the (correct) total DOS.

Giovanni

-- 

Giovanni Cantele, PhD
CNR-SPIN
c/o Dipartimento di Fisica
Universita' di Napoli "Federico II"
Complesso Universitario M. S. Angelo - Ed. 6
Via Cintia, I-80126, Napoli, Italy
e-mail: giovanni.cantele at spin.cnr.it
Phone: +39 081 676910
Skype contact: giocan74

ResearcherID: http://www.researcherid.com/rid/A-1951-2009
Web page: http://people.na.infn.it/~cantele

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20140404/b1f7f911/attachment.html>