[CP2K-user] [CP2K:12813] Band alignment calculations

[Elham M.Goliaei]

Dear Patrick,

    Thanks a lot.
All the best,
Elham


On Fri, Jan 24, 2020 at 12:47 AM Patrick Gono <patri... at gmail.com>
wrote:

> Dear Elham,
>
> You need two calculations. A bulk calculation where you align the band
> edges with respect to the average electrostatic potential. And a slab
> calculation with vacuum, where you align the average electrostatic
> potential in the center layers of the slab with respect to the vacuum
> potential.
>
> In CP2K, the average electrostatic potential over the whole cell is set to
> zero. Hence, the bulk calculation only consists in running a CELL_OPT of a
> big enough supercell, and taking the values of the Fermi level and the
> HOMO-LUMO gap. The Fermi level represents the position of the valence band
> with respect to the average electrostatic potential, and the Fermi level +
> gap is then the conduction band. This calculation gives you the alignment
> of the band edges with respect to the average electrostatic potential.
>
> For the vacuum calculation, you have to make sure you have a thick enough
> slab (so that the electrostatic potential in the middle layers behaves like
> the bulk one) and a thick enough vacuum layer, so that there the potential
> is flat. Run a GEO_OPT of the slab with vacuum, and then perform an ENERGY
> calculation on the resulting geometry with the V_HARTREE_CUBE option in the
> PRINT section inside DFT set to .TRUE.
> Next, project the .cube file of the average potential along the axis
> perpendicular to the interface. Then, take the value in the middle of the
> vacuum region, and subtract the average over the central-most layer(s)
> inside the slab. This gives you the alignment of the average electrostatic
> potential with respect to vacuum.
>
> You see now that combining the results of the two yields the desired
> alignment.
>
> Yours sincerely,
> Patrick Gono
>
> On Thu, 23 Jan 2020 at 14:27, Elham M.Goliaei <e.go... at gmail.com> wrote:
>
>> Hi Patrick,
>>     Thanks, it was informative, first, I wanna calculate band alignment
>> versus vacuum, for example according to Fig. 1;
>> https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.102.036402
>>
>> How can I do these calculation to get band alignment versus vacuum?
>>
>> All the best,
>> Elham
>>
>>
>>
>>
>>
>> On Wed, Jan 22, 2020 at 6:33 AM Patrick Gono <patri... at gmail.com>
>> wrote:
>>
>>> Dear Elham,
>>>
>>> In the work of Guo et al. referenced above, it is stated that a
>>> molecular dynamics simulation at the level of PBE was performed at the
>>> desired temperature. The projected density of states was averaged over the
>>> duration of the simulation. Since the average PDOS has long tails at the
>>> band edges, a linear extrapolation of the band edge PDOS was carried out.
>>> It is these values that are used as the temperature corrected band edges.
>>> See Fig. 3 of this paper by Wiktor et al.:
>>> https://journals.aps.org/prmaterials/abstract/10.1103/PhysRevMaterials.1.022401
>>>
>>> It is possible that you require the use of a more advanced electronic
>>> structure method, and hence ab initio molecular dynamics may not be
>>> feasible. In that case, you can follow the approach outlined in the above
>>> reference -- run MD at the semilocal level, select a set of configurations
>>> from the trajectory, perform single point (ENERGY) calculations with your
>>> desired method, compute the PDOS, average over all snapshots, and carry out
>>> the linear extrapolation of the PDOS tails around the band gap mentioned
>>> previously.
>>>
>>> Alternatively, a one shot calculation of the phonon spectrum can be used
>>> to estimate the band gap renormalization due to finite temperature. See the
>>> work by Prof. Giustino, for example:
>>> https://journals.aps.org/prb/abstract/10.1103/PhysRevB.94.075125
>>>
>>> Hope this helps.
>>> Yours sincerely,
>>> Patrick Gono
>>>
>>> On Wed, 22 Jan 2020 at 14:39, Elham M.Goliaei <e.go... at gmail.com>
>>> wrote:
>>>
>>>> Thanks, can you guide me how I  can calculate T-dependent corrections
>>>> of the band edges (Eq. 4 and 5).
>>>>
>>>> All the best,
>>>> Elham
>>>>
>>>>
>>>>
>>>> On Tue, Jan 21, 2020 at 4:27 AM Patrick Gono <patri... at gmail.com>
>>>> wrote:
>>>>
>>>>> Dear Elham,
>>>>>
>>>>> I recommend the work by Guo et al. where the band alignment at the
>>>>> semiconductor water interface is studied in detail:
>>>>> https://pubs.acs.org/doi/abs/10.1021/acs.chemmater.7b02619
>>>>>
>>>>> Yours sincerely,
>>>>> Patrick Gono
>>>>>
>>>>> On Mon, 20 Jan 2020 at 11:07, Elham M.Goliaei <e.go... at gmail.com>
>>>>> wrote:
>>>>>
>>>>>> Hi Matthias,
>>>>>>
>>>>>>    I wanna calculate band alignment of a semiconductor and band
>>>>>> alignment at the semiconductor-water interface, can you guide me how to
>>>>>> calculate.
>>>>>>
>>>>>> All the best,
>>>>>> Elham
>>>>>>
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