[CP2K-user] Fermi energy too high?
Matt W
mattwa... at gmail.com
Wed Jan 16 09:26:32 UTC 2019
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
>>>>>>>>>>
>>>>>>>>>
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