[CP2K-user] Fermi energy too high?

Phil G. phil... at aol.com
Tue Jan 15 08:52:35 CET 2019


Hello again,

have tried some attempts to start calculation with WAVELET poisson solver, 
but all attempts have failed due to following error messages:

1)  the FFT in the x direction is not allowed
     n01 dimension         154
     (pw/ps_wavelet_util.F:358)

     ===== Routine Calling Stack ===== 

           13 S_FFT_dimensions
           12 RS_z_slice_distribution
           11 ps_wavelet_create
     the FFT in the x direction is not allowed
     n01 dimension         154
           10 pw_poisson_rebuild
            9 pw_poisson_solve
            8 qs_ks_build_kohn_sham_matrix
            7 rebuild_ks_matrix
     the FFT in the x direction is not allowed
     n01 dimension         154
     the FFT in the x direction is not allowed
     n01 dimension         154
     the FFT in the x direction is not allowed
     n01 dimension         154
     the FFT in the x direction is not allowed
     n01 dimension         154
            6 qs_ks_update_qs_env
            5 scf_env_do_scf_inner_loop
            4 scf_env_do_scf
            3 qs_energies
            2 qs_forces
            1 CP2K


2)  after that I turn off the command EXTENDED_FFT_LENGTHS, then:

    Index to radix array not found.
    (pw/fft_tools.F:293)

     ===== Routine Calling Stack ===== 

            6 pw_grid_setup
            5 pw_env_rebuild
            4 qs_env_rebuild_pw_env
            3 qs_env_setup
            2 qs_init_subsys
            1 CP2K


That's strange and I don't know what to do. 
In my input file there are some info about commands:

[...]
    SURFACE_DIPOLE_CORRECTION .TRUE.
    SURF_DIP_DIR Y
[...]
    &MGRID
      CUTOFF 600
      NGRIDS 5
      REL_CUTOFF 50
    &END MGRID
[...]
    &POISSON
      POISSON_SOLVER WAVELET
      PERIODIC XZ
    &END POISSON
[...]

[...]
    &CELL
      A    5.148      0.0         0.0
      B    0.000      100.0      0.0
      C    0.0          0.0         8.9166         
      PERIODIC XZ
    &END CELL
[...]

Phil


Am Donnerstag, 10. Januar 2019 10:56:24 UTC+1 schrieb Phil G.:
>
> Dear Matt,
>
> how can find the potential in the vacuum (which type of potential? 
> potential energy or electric/electrostatic potential?) ?
> For the case of electric/electrostatic potential, there is a flat curve 
> with a step near the vacuum center as a consequence of dipole correction in 
> Z direction, while in the bulk slab there is a periodic curve. 
>
> I will try to use the wavelet solver with PERIODIC XY.
>
> Phil
>
> Am Mittwoch, 9. Januar 2019 14:05:04 UTC+1 schrieb Matt W:
>>
>> Hello again,
>>
>> did you find the potential in the vacuum and align to that? You need to 
>> set a reference to get absolute values.
>>
>> You could also try using the wavelet solver 
>>
>> &POISSON
>>    PSOLVER WAVELET
>>    PERIODIC XZ
>> &END
>>
>> and PERIODIC XZ  in the &CELL section. The Y direction must be the 
>> non-periodic one. That gives an absolute reference (if there is no dipole 
>> in the cell otherwise you need the  dipole correction switched on).
>>
>> Matt
>>
>> On Wednesday, January 9, 2019 at 8:18:58 AM UTC, Phil G. wrote:
>>>
>>> Dear Matt,
>>>
>>> thank you for your reply and good suggestions. Now I have let different 
>>> LiNbO3 slab systems to be calculated:
>>>
>>> a) 14 trilayer system as from Sanna et al., *Appl. Surf. Sci.* *301* 
>>> (2014), 70-78 with Nb-O3-Li2 surface termination on the one side of the 
>>> slab and Li-O surface termination on the other side. Vacuum space of at 
>>> least 40 Angstroms was included. The bulk region was already 
>>> geometry-optimized and bulk atoms were fixed in the inner 6 trilayers. 
>>> Geometry optimization on the whole slab system was performed and then the 
>>> pdos of the system was calculated and plotted for every atom layers.
>>> Result: E_F = 0.1552 eV  (fermi energy is overall constant, in every 
>>> atom layers)
>>>
>>> b) the same as a), but the bulk region was not already 
>>> geometry-optimized before. Geometry optimization was performed and 
>>> calculation of pdos.
>>> Result: E_F = - 0.8516 eV
>>>
>>> c) the same as b), but 26 trilayers instead of 14 trilayers. Geometry 
>>> optimization and calculation of pdos were performed.
>>> Result: E_F = 2.3372 eV
>>>
>>>
>>> So, I am wondering why these values differ so much. Should I need band 
>>> structure calculation of the bulk LiNbO3 in order to find the global 
>>> valence band edge maximum (with KPOINT calculation)?
>>>
>>> Kind regards,
>>>
>>> Phil
>>>
>>>
>>> Am Freitag, 14. Dezember 2018 17:41:03 UTC+1 schrieb Matt W:
>>>>
>>>> In a periodic system the zero of the one electron levels is arbitrary. 
>>>> If you need a reference you need to run a slab calculation with vacuum or 
>>>> try to align semi-core states to something.
>>>>
>>>> Matt
>>>>
>>>> On Friday, December 14, 2018 at 4:33:13 PM UTC, Phil G. wrote:
>>>>>
>>>>> Dear people and experts of CP2K,
>>>>>
>>>>> after the geometry optimization of the lithium niobate (LiNbO3) unit 
>>>>> cell I would like to obtain pdos in order to determine the band gap and 
>>>>> Fermi energy of the bulk system.
>>>>> After the calculation with ENERGY_FORCE I got pdos files of the three 
>>>>> atoms (indexing depends on the z-position of the atoms) and I'm wondering 
>>>>> about the value of Fermi energy: E_F = 0.300174 a.u. which is 8.168 eV. Is 
>>>>> that not too high? And which energy has the value 0 and what is the 
>>>>> reference? What is the Fermi energy defined in the language of CP2K?
>>>>> The energy band gap (HOMO-LUMO gap) of 3.62 eV agrees well with 
>>>>> experimental values of 3.7 to 3.9 eV. But I cannot imagine that Fermi level 
>>>>> has too high energy values.
>>>>>
>>>>> Has anyone an idea what is the reason for such high Fermi energy 
>>>>> values?
>>>>>
>>>>> Here the input and output files are attached here.
>>>>>
>>>>> Kind regards,
>>>>>
>>>>> Phil
>>>>>
>>>>
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