[QE-users] General problems in calculation and interpretation of PDOS

[Giuseppe Mattioli]

Dear Parisa

> 1-    PDOS refers to partial density of states or projected density of
> states or they both are equivalent.

The Kohn-Sham Orbitals are projected on the atomic pseudowavefunction  
generated with (and contained in) the pseudopotential. You may read  
the original papers (Kleinman-Bylander, Martins-Troullier, Vanderbilt,  
Kresse-Joubert, all published on Phys. Rev. B if I remember well) if  
you want more insight.

> 2-    How can I get more insight about spherical harmonics? Would you give
> a reference to read more about?

If you need an information more basic than that provided by the above  
papers, then you should read a quantum-mechanics book.

  > 3-    In the beginning of the file “pdos.out” we see “atomic states used
> for projection”. In case of BaTiO3 the number of states is 30. What does
> this 30 mean? Number of valence electron or …. . Does this number depend to
> the exploited psudopotential?

They are read from the pseudopotential. Their meaning should be quite  
clear. In the case below, the code is projecting on a Fe atom with  
valence configuration 3s, 3p, 4s, 3d

      Atomic states used for projection
      (read from pseudopotential files):

      state #   1: atom   1 (Fe ), wfc  1 (l=0 m= 1)
      state #   2: atom   1 (Fe ), wfc  2 (l=1 m= 1)
      state #   3: atom   1 (Fe ), wfc  2 (l=1 m= 2)
      state #   4: atom   1 (Fe ), wfc  2 (l=1 m= 3)
      state #   5: atom   1 (Fe ), wfc  3 (l=0 m= 1)
      state #   6: atom   1 (Fe ), wfc  4 (l=2 m= 1)
      state #   7: atom   1 (Fe ), wfc  4 (l=2 m= 2)
      state #   8: atom   1 (Fe ), wfc  4 (l=2 m= 3)
      state #   9: atom   1 (Fe ), wfc  4 (l=2 m= 4)
      state #  10: atom   1 (Fe ), wfc  4 (l=2 m= 5)

> 4-    In the manual of QE, (
> https://www.quantum-espresso.org/Doc/INPUT_PROJWFC.html), ln the section
> “order of orbital”, l and m are not clearly described, at least for me, it
> is not clear that what these numbers mean.
> for l=1:
>     1 pz     (m=0)
> 2    px     (real combination of m=+/-1 with cosine)
>        3 py     (real combination of m=+/-1 with sine)
> 5-    as a result of pdos for barium we see 4 files namely:
>
> *.pdos_atm#1(Ba)_wfc#1(s)
> *.pdos_atm#1(Ba)_wfc#2(s)
> *.pdos_atm#1(Ba)_wfc#3(p)
> *.pdos_atm#1(Ba)_wfc#4(p)
>
> While 8 atomic states (for barium) have been taken into account for
> projection and now we just see 4 files. How do we interpret these
> differences? Would you please kindly comment on these question?

I suppose that the Ba pseudopotential has been generated with 5s, 5p,  
6s and 6p as valence shells with 10 valence electrons, with the 5d  
shell embedded into the core pseudopotential. You will find the total  
projection (or spin up/down projections) in the (Ba)_wfc#1(s) and  
(Ba)_wfc#2(s) files, and more columns corresponding to total p, px, py  
and pz orbitals in the (Ba)_wfc#3(p) and (Ba)_wfc#4(p) files.

HTH
Giuseppe

Parisa alipour kamran <p.alipourkamran at gmail.com> ha scritto:

> Dear Users,
>
> I study the strain effect on the band structure of Barium Titanate (BaTiO3)
> using QE in my master thesis. I used projwfc.x in order to make pdos.
> Regarding our output files I have some questions, although these questions
> may become elementary for you and they have been briefly described in QE
> manual but I would prefer to get deeper insight, rather than using the code
> as a black box.
>
> 1-    PDOS refers to partial density of states or projected density of
> states or they both are equivalent.
> 2-    How can I get more insight about spherical harmonics? Would you give
> a reference to read more about?
> 3-    In the beginning of the file “pdos.out” we see “atomic states used
> for projection”. In case of BaTiO3 the number of states is 30. What does
> this 30 mean? Number of valence electron or …. . Does this number depend to
> the exploited psudopotential?
> 4-    In the manual of QE, (
> https://www.quantum-espresso.org/Doc/INPUT_PROJWFC.html), ln the section
> “order of orbital”, l and m are not clearly described, at least for me, it
> is not clear that what these numbers mean.
> for l=1:
>     1 pz     (m=0)
> 2    px     (real combination of m=+/-1 with cosine)
>        3 py     (real combination of m=+/-1 with sine)
> 5-    as a result of pdos for barium we see 4 files namely:
>
> *.pdos_atm#1(Ba)_wfc#1(s)
> *.pdos_atm#1(Ba)_wfc#2(s)
> *.pdos_atm#1(Ba)_wfc#3(p)
> *.pdos_atm#1(Ba)_wfc#4(p)
>
> While 8 atomic states (for barium) have been taken into account for
> projection and now we just see 4 files. How do we interpret these
> differences? Would you please kindly comment on these question?
>
>
>
> Kind Regards,
>   Parisa



GIUSEPPE MATTIOLI
CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
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E-mail: <giuseppe.mattioli at ism.cnr.it>