[CP2K-user] Fermi energy too high?
Matt W
mattwa... at gmail.com
Wed Jan 16 13:20:18 UTC 2019
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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