[CP2K-user] Fermi energy too high?

Matt W mattwa... at gmail.com
Tue Jan 15 11:31:21 CET 2019


Ah, OK. The extended FFT lengths only works with FFTW not with the wavelet 
FFT.

You do not need such a large vacuum with the wavelet solver as it is 
genuinely non-periodic. Place the slab in the center and 5A of vacuum 
either side should be sufficient - allow 10 A either side to get a clear 
decay to vacuum level(s). You will get two vacuum levels if you have  a 
dipole. I don't know if wavelet will work with the dipole correction, I'd 
turn it off to start with.

Matt

On Tuesday, January 15, 2019 at 8:52:35 AM UTC, Phil G. wrote:
>
> 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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