[QE-users] Lithium Niobate Hubbard Calculations

[Mona Asadinamin]

Dear all;


And I am trying to reproduce the results for NbLi(SLN) of this paper:


PHYSICAL REVIEW MATERIALS 1, 054406 (2017)


  Although I could calculate the band structure of the plain lithium niobate, I have some difficulties in my Hubbard calculations and I really appreciate it if you could please guide me through that.



   Nb sits in Li site with +5 charge, but since Li already has +1, I defined the total charge of the unit cell as +4. I am also setting the occupations of the substitutional Nb manually, so that I have 4 spin ups and zero spin downs. (I have attached my input file)

    Below, is a section of my output. Although the occupations are set to the manual ones, after a scf iteration, it changes to incorrect and partial occupations! Also, the number of orbitals treated with Hubbard term is printed as 3 whereas it should be 4!


Output:


Before scf:


LDA+U parameters:

U( 1)     =  4.00000000

alpha( 1) =  0.00000000

atom    8   Tr[ns(na)] (up, down, total) =   4.00000  0.00000  4.00000

   spin  1

    eigenvalues:

  0.000  1.000  1.000  1.000  1.000

    eigenvectors:

  1.000  0.000  0.000  0.000  0.000

  0.000  0.011  0.235  0.086  0.669

  0.000  0.178  0.176  0.637  0.008

  0.000  0.018  0.588  0.072  0.322

  0.000  0.793  0.001  0.206  0.001

    occupations:

  0.000 -0.000  0.000  0.000  0.000

 -0.000  1.000  0.000  0.000  0.000

  0.000  0.000  1.000 -0.000 -0.000

  0.000  0.000 -0.000  1.000  0.000

  0.000  0.000 -0.000  0.000  1.000

   spin  2

    eigenvalues:

  0.000  0.000  0.000  0.000  0.000

    eigenvectors:

  1.000  0.000  0.000  0.000  0.000

  0.000  1.000  0.000  0.000  0.000

  0.000  0.000  1.000  0.000  0.000

  0.000  0.000  0.000  1.000  0.000

  0.000  0.000  0.000  0.000  1.000

    occupations:

  0.000  0.000  0.000  0.000  0.000

  0.000  0.000  0.000  0.000  0.000

  0.000  0.000  0.000  0.000  0.000

  0.000  0.000  0.000  0.000  0.000

  0.000  0.000  0.000  0.000  0.000

atomic mag. moment =     4.000000

N of occupied +U levels =    4.000000



After scf:


LDA+U parameters:

U( 1)     =  4.00000000

alpha( 1) =  0.00000000

atom    8   Tr[ns(na)] (up, down, total) =   3.57808  1.74127  5.31935

   spin  1

    eigenvalues:

  0.503  0.503  0.802  0.885  0.885

    eigenvectors:

  0.000  0.000  1.000  0.000  0.000

  0.068  0.489  0.000  0.047  0.397

  0.489  0.068  0.000  0.397  0.047

  0.080  0.364  0.000  0.090  0.466

  0.364  0.080  0.000  0.466  0.090

    occupations:

  0.802 -0.000 -0.000 -0.000 -0.000

 -0.000  0.673 -0.000 -0.189 -0.016

 -0.000 -0.000  0.673 -0.016  0.189

 -0.000 -0.189 -0.016  0.715  0.000

 -0.000 -0.016  0.189  0.000  0.715

   spin  2

    eigenvalues:

  0.266  0.266  0.271  0.469  0.469

    eigenvectors:

  0.000  0.000  1.000  0.000  0.000

  0.047  0.467  0.000  0.055  0.432

  0.467  0.047  0.000  0.432  0.055

  0.079  0.408  0.000  0.097  0.416

  0.408  0.079  0.000  0.416  0.097

    occupations:

  0.271 -0.000 -0.000 -0.000 -0.000

 -0.000  0.365 -0.000  0.101  0.011

 -0.000 -0.000  0.365  0.011 -0.101

 -0.000  0.101  0.011  0.370  0.000

 -0.000  0.011 -0.101  0.000  0.370

atomic mag. moment =     1.836805

N of occupied +U levels =    5.319347



When I plot the band structure, the overall valence and conduction bands do not look bad (although not similar), and I see three dispersion less bands in the gap!


I am very confused. I tried larger U values but it does not help. I also tried scf after doing vc-relax, but I get the same results. I tried larger ecuts and kpoints, but still the same thing happens.

I appreciate any comments or suggestions.


Best regards;

Mona Asadi Namin
Graduate student
Center for simulational physics
University of Georgia
--------------------------------------
Email:mona.a at uga.ed<mailto:mona.a at uga.edu>u<mailto:mona.a at uga.edu>
Phone: +1-215-906-23-92

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