[CP2K-user] Fermi energy too high?
Phil G.
phil... at aol.com
Mon Jan 21 11:25:54 UTC 2019
Dear Matt,
thank you very much for the suggestions and after some tests it also worked
! :-)
To check the effect of dipole correction on the calculation, I started
different slab systems and used cell length in y-direction at 50 Angstrom
(much more than this value will lead to error (index to radix array not
found)):
The slab systems are defined as in the first message above (9th January)
a) without dipole correction: E_F = -3.31475 eV
with dipole correction: E_F = -3.2983 eV
b) without dipole correction: E_F = -4.642 eV
with dipole correction: E_F = -4.72 eV
It seems that the dipole correction leads to a marginal reduction of the
Fermi energy.
Now I want to check, if the vacuum level has another value that the Fermi
energy as you showed (+/- 0.75 eV) by plotting pdos as a function of atom
coordinates, i.e. in slab y-direction.
Thanks again for your helpful suggestions! :-)
Kind regards,
Phil
Am Mittwoch, 16. Januar 2019 14:20:18 UTC+1 schrieb Matt W:
>
> I added
>
> &CENTER_COORDS
> &END
>
> in the topology section. I get the 'fermi level' reported at -4.61 eV. And
> the vacuum levels at +- 0.75 eV
>
> So the work functions of the two faces are ~5.4 and 3.8 eV respectively. I
> got the profile of the potential by adding &V_HARTREE_CUBE and using the
> cubecruncher utility (bundled in the tools directory) to extract the
> averaged y profile to find the vacuum levels.
>
> Matt
>
>
>
> On Wednesday, January 16, 2019 at 9:26:32 AM UTC, Matt W wrote:
>>
>> 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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