[CP2K-user] Fermi energy too high?

[Matt W]

Hi,

the xyz file you sent doesn't have the y coords centred in the cell. The 
cell goes from 0 to L. You centre as if it goes from -L/2 to L/2.

If you print V_HARTREE_CUBE you can work out the potential profile across 
the slab. 

BTW your slab is too small in X and Z for reliable results without k-point 
sampling...

Matt

On Wednesday, January 16, 2019 at 8:54:56 AM UTC, Phil G. wrote:
>
> yes, the slab was centered in y-direction (xyz file attached here), but in 
> x- and z- direction from 0 to the corresponding lengths of the slab.
> Maybe I should extend the size of vacuum space or turn on the dipole 
> correction?
> For searching for reason, the input file is also attached here.
>
> Phil
>
> Am Dienstag, 15. Januar 2019 16:07:55 UTC+1 schrieb Matt W:
>>
>> Is your slab in the centre of the cell (Y direction)? -  the cell runs 
>> from 0 to L, so the slab must be centred at L/2.
>>
>> Matt
>>
>> On Tuesday, January 15, 2019 at 2:21:26 PM UTC, Phil G. wrote:
>>>
>>> Dear Matt,
>>>
>>> thank you for the suggestions and after centering the slab in 
>>> y-direction and turning off the surface dipole correction, the program 
>>> finally runs and I get the result, but there are some error messages such 
>>> as:
>>>
>>>  *** WARNING in pw/ps_wavelet_methods.F:236 :: Density non-zero on the 
>>> ***
>>>  *** edges of the unit cell: wrong results in WAVELET solver           
>>> ***
>>>
>>>     89 Broy./Diag. 0.10E+00    2.3     0.00000880     -3020.8753805067  
>>> 4.85E-05
>>>
>>>   *** SCF run converged in    89 steps ***
>>>
>>> I have chosen the cell length of 40 angstroms in Y direction (slab 
>>> length in y-direction is about 27.6 angstroms).
>>> For the LiNbO3 slab consisting of 14 trilayers as stated in the message 
>>> of 9th January, I obtain the result of the Fermi energy:
>>>
>>>   E_F = 11.174 eV    (in comparison to the -0.8516 eV in case b) )
>>>
>>> This is unrealistic...should I have to enlarge the cell length in 
>>> y-direction or should I turn on the dipole correction?
>>>
>>> Phil
>>>
>>>
>>>
>>> Am Dienstag, 15. Januar 2019 12:31:22 UTC+1 schrieb Matt W:
>>>>
>>>> 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
>>>>>>>>>>
>>>>>>>>>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.cp2k.org/archives/cp2k-user/attachments/20190116/3f0d5755/attachment.htm>