ABINIT Discussion Forums

Dear colleagues,

in the PHDOS file which one obtains with anaddb, besides omega and PHDOS columns, there are other columns named PJDOS[1] and so on. What is their meaning? Are these projected PHDOSs on atoms? I see that their sum gives the PHDOS column.

Thank you in advance!

Yours,

Igor Lukacevic

Dear colleagues,

I apologize if my previous post was too scarce and not following the nettiquette.

We're trying to find out the projected phonon DOS. I found several papers mentioning PPDOS, but neither of them explained the method of how they did it (except the routines not yet implemented in 2008). Since we're using 5.8.4 version, we've searches the tests from the latest version, but there is also no mention of PPDOS calc.

When we plot PJDOS columns with PHDOS together, they could look like PPDOS on atoms, but we're not certain. They look like those of PbS from Cardona et aql. papers, but we're not sure if the same arguments can be applied to our case of BaO.

Could anyone confirm to us this fact?

Thank you in advance!

Igor Lukacevic

Well, at that time we hack the thm9.F90 subroutine in the Src_7bb (5.x directory file), now it is 77_ddb for version 6.x. It was rather easy because it was calculated already in the subroutine and we had just to
print it out and normalize it correctly. In the new version, I really do not know if it is print it. Let see if one of the guys replies. I did try to find my
old version but was not able to.. at least for now.. but I just remember you had to follow the variable ggij within that subroutine... please if you are unable to do it or you do not get
any reply from the experts I can trace my version... but it will take few days.. I have so many versions ..

let me know

"Gandalf, you old fool!"

Dear Aldo, thnx for the help. I found the subroutine, and the part (I think I did) where it starts to print dos (is it the part just before the calculation of the thermodynamic functions?). I cannot find the part which orders to print the PHDOS file, thou.
Just now I looked at the header of the PHDOS file, which I obtain with prtdos variable in the anaddb. It says

#
# Phonon density of states and projected DOS generated by anaddb
#
# energy in Ha , DOS in states/Ha
# Gaussian method with smearing = 2.27816763E-05Ha , nqibz = 408
#
# omega PHDOS IPHDOS PJDOS[1] IPJDOS[1] ...
#

If this is so, does it mean that PJDOSs' are indeed projected PDOSs'?

Thanks again!

Igor Lukacevic

it seems like.. you can check that because basically the sum over atoms should give you the total density of states... and of course,
some physical intuition also helps. Let me know if I can help in something else.

Regards

Thanks again, I think that solves the matter.

But still cannot find the part af the code which prints PHDOS file when prtdos variable is set in anaddb input. Any help here?

Cheers!

Igor Lukacevic

I have not use this one but tracking the variable I can see that most calculations are done in 77_ddb/mkphdos.F90, probably there are printed on the
"screen" or in the logout file if you are piping the result. Let me know, it seems you can now use the tetrahedron method to obtain the vDOS.. that is really neat!

The PHDOS file is written in the routine print_phondos contained in the module 77_ddb/m_phdos.F90

The values reported in the PJDOS columns represent the contribution to the total phonon DOS given by the subset of atoms of the same TYPE.
PJDOS[1] is the contribution due to the atoms of type #1, IPJDOS[1] is the integral of PJDOS[1]

Matteo

Dear Matteo,

thank You for the clarification. That's all I wanted to know.

Igor Lukacevic

Hi Igor,

I got a question about PHDOS file. I have some negative values of omega. I am kind of confused why anaddb gives such negative values. I am just trying to figure out this problem why it is happening.

I would appreciate if you have any idea about it to share.

Thanks,

Suvas
-1.94062299E-03 1.07737515E-11 3.68166157E-18 7.00448096E-12 2.39360713E-18 3.76927051E-12 1.28805444E-18
-1.93971172E-03 1.47326937E-11 1.93446488E-17 9.57838141E-12 1.25768138E-17 5.15431232E-12 6.76783495E-18
-1.93880045E-03 2.01148457E-11 3.69108941E-17 1.30775875E-11 2.39974388E-17 7.03725821E-12 1.29134552E-17
-1.93788918E-03 2.74202061E-11 6.18980230E-17 1.78271783E-11 4.02427581E-17 9.59302779E-12 2.16552649E-17
-1.93697792E-03 3.73202308E-11 9.59067177E-17 2.42637086E-11 6.23534750E-17 1.30565222E-11 3.35532427E-17
-1.93606665E-03 5.07151431E-11 1.42121754E-16 3.29724703E-11 9.24001991E-17 1.77426728E-11 4.97215550E-17
-1.93515538E-03 6.88098883E-11 2.04825935E-16 4.47368762E-11 1.33167438E-16 2.40730122E-11 7.16584965E-17
-1.93424412E-03 9.32146233E-11 2.89769345E-16 6.06037957E-11 1.88393677E-16 3.26108276E-11 1.01375668E-16
-1.93333285E-03 1.26077439E-10 4.04659555E-16 8.19698485E-11 2.63090095E-16 4.41075907E-11 1.41569459E-16
-1.93242158E-03 1.70259355E-10 5.59811286E-16 1.10695181E-10 3.63962961E-16 5.95641736E-11 1.95848325E-16
-1.93151032E-03 2.29564644E-10 7.69005970E-16 1.49253222E-10 4.99972497E-16 8.03114218E-11 2.69033474E-16
-1.93059905E-03 3.09043473E-10 1.05062709E-15 2.00927450E-10 6.83071051E-16 1.08116023E-10 3.67556037E-16
9.95479289E-04 7.75218121E+03 1.14423779E+01 4.15402618E+03 6.00402258E+00 3.59815502E+03 5.43835531E+00
9.96390556E-04 7.72021283E+03 1.14494131E+01 4.14141602E+03 6.00779651E+00 3.57879681E+03 5.44161655E+00
9.97301823E-04 7.68909692E+03 1.14564199E+01 4.12899371E+03 6.01155913E+00 3.56010322E+03 5.44486075E+00
9.98213090E-04 7.65891259E+03 1.14633992E+01 4.11679571E+03 6.01531063E+00 3.54211687E+03 5.44808857E+00
9.99124357E-04 7.62974571E+03 1.14703519E+01 4.10486165E+03 6.01905125E+00 3.52488406E+03 5.45130068E+00
1.00003562E-03 7.60168827E+03 1.14772791E+01 4.09323391E+03 6.02278128E+00 3.50845436E+03 5.45449782E+00
1.00094689E-03 7.57483761E+03 1.14841818E+01 4.08195730E+03 6.02650104E+00 3.49288031E+03 5.45768076E+00
1.00185816E-03 7.54929564E+03 1.14910612E+01 4.07107862E+03 6.03021088E+00 3.47821702E+03 5.46085035E+00
1.00276942E-03 7.52516802E+03 1.14979187E+01 4.06064629E+03 6.03391121E+00 3.46452173E+03 5.46400745E+00

You are getting negative frequencies in the PHDOS file because there are regions of the BZ where
the phonon frequencies obtained via the Fourier interpolation of the interatomic force constants are
negative (purely imaginary, to be more precise).
The routine takes into account this possibility and it defines the frequency mesh so that it encloses the minimum and
the maximum phonon frequency obtained on the input q-mesh.
You may want to plot your phonon band structure along a high symmetry q-path
to understand where these vibrational instabilities are occuring.

Matteo

Dear suvas,

please, follow Matteo's advice, if you want to get more information about the lattice dynamics of your system.

Why it happens is hard to answer at this moment. It could be convergence wrt ecut or ngkpt, lattice instability, "wrong" functional...

Igor

Dear Igor/gmatteo,

Thanks for your helpful suggestion. I have really high ecutoff 80 which is high enough for convergence test. Actually I checked by plotting total energy with ecutoff.
The ngkpt is also very high around 80 80 80. I also tried with higher values, still problem remains same. I checked phonon frequency(phonon band structure) in different symmetry points. It shows that negative frequency (instabillity) is seen in gamma point or close to gamma point. Anaddb corrects negative frequency only at gamma point. But frequencies are still negative to those points which are close to gamma point. As Igor suggested, I will try with different exchange correlation.

I once gain appreciate to both of you.

Suvas

Dear suvas,

1] ngkpt is 80 80 80?! Is this a typo?

2] Convergence of total energy does not necessarily ensure the convergence of phonon frequencies. You have to check whether your phonon freqs are converged.

3] From what you said, it may be that your system has a lattice instability at the Gamma point.

Cheers!

Igor

Hello,


Have you relaxed your system to equilibrium before doing phonon frequencies ? If not, that might explain your negative answers.


David