[QE-users] tutorial for the FCP method

Mon Apr 11 23:51:15 CEST 2022

Dear Minoru,

Thank you very much for taking the time to explain these examples in 
detail. If you don't mind I have a few followup questions:

1) for the first case, the ESM calculation: how does one determine the 
vacuum region? In a regular slab calculation, as far as my understanding 
goes, one increases the vacuum region until there is little interaction 
between the periodical neighbors as it were. In this case, I have 
performed two calculations for 10 A of vacuum on either side of the slab 
and then for 5 A. The latter case had a lower total energy than the 
former. Is this normal? I have also tried a rather large 30 A on either 
side, but the calculation failed to converge.

2) also for the ESM case: do I understand correctly that for the 
metal-slab-metal case, one controls the Hartree potential using 
esm_efield and for the vacuum-slab-metal case one uses the tot_charge 
parameter?

I am trying to make that the Hartree potential for my slab with 
ferroelectric layers is correct as the following article suggests:

https://www.nature.com/articles/s41524-021-00529-1

They are using a different method and I believe that a combination of 
ESM and FCP could accomplish the same result for my case. That is why my 
next question is regarding FCP:

3) in FCP one has to provide the target_mu. In your example you use the 
Fermi level from the ESM calculation in the first example as the target 
mu in the FCP calculation. Is this the route that must be used?

Thank you again for your time!

Best regards,

Lucian

On 11/04/2022 16:16, Otani Minoru wrote:
> Dear Lucian,
>
> I made those examples in PW/examples/ESM_example directory. Here, I am 
> going to explain the purpose of each examples.
>
> 1) ESM
> One can understand the overall usage of the effective screening medium 
> (ESM) method. More precisely, when you plot the esm1 file, you can see 
> the difference of the calculated electrostatic potentials depending on 
> the boundary conditions, i.e., pbc, bc1, bc2, and bc3. By changing the 
> parameter "tot_charge", you can see how the Fermi energy changes in a 
> Constant-N calculation: Constant-N means that we fix the total number 
> of electron (N) during the SCF calculation. If you want to understand 
> more detail about the method and configuration of the slab model, 
> please read the original paper:
> Physical Review B 73, 115407 (2006)
>
> 2) FCP & 3) GCSCF
> Unlike the Constant-N calculation, the second (FCP) and the third 
> (GCSCF) examples, we can conduct an electronic structure calculation 
> with fixed chemical potential for electron (constant-mu). FCP stands 
> for fictitious charge particle and the original paper is the following:
> Physical Review Letters 109, 266101 (2012).
> GCSCF is the abbreviation for the grand canonical SCF and the original 
> paper is below:
> J. Chem. Phys. 146, 114104 (2017).
>
> You can find the difference between FCP and GCSCF calculations in the 
> following paper:
> Physical Review Materials 5, 065001 (2021).
> As stated in the paper, FCP and GCSCF have their advantages in the 
> constant-mu calculations. Thus we have implemented both methods for 
> users convenience.
>
> Best regards,
> Minoru
>
> --------------------------------------------------------------------------------------------------------
> Minoru Otani, Ph.D., Professor
> Center for Computational Sciences and Faculty of Pure and Applied 
> Sciences,
> University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8577, Japan
> TEL: +81-29-853-4273
> FAX: +81-29-853-6406
> E-mail: otani at ccs.tsukuba.ac.jp <mailto:otani at ccs.tsukuba.ac.jp>
> Web: https://www2.ccs.tsukuba.ac.jp/public/otani/
> --------------------------------------------------------------------------------------------------------
>
>
>> On Apr 11, 2022, at 15:48, Lucian D. Filip <lucian.filip at infim.ro> wrote:
>>
>> Hello all,
>>
>> Is there a tutorial out there that explains in detail how to use the 
>> FCP method? I have read the one in the PW/examples on github but I 
>> can't figure out what it is trying to accomplish.
>>
>> It is split into three types of calculations: 1) ESM calculation; 2) 
>> FCP calculation; 3) GCSCP calculation. Why is that? Are they related? 
>> Is this the order one is supposed to use to obtain a what exactly?
>>
>> Can someone explain the purpose of each steps taken in this example?
>>
>>
>> Thank you!
>>
>>
>> Lucian
>>
>> -- 
>> Dr. Lucian Dragos Filip
>> National Institute of Materials Physics
>> Atomistilor str. 405A
>> PO Box MG. 7
>> Magurele, 077125
>> Bucharest, Romania
>> E-mail:   lucian.filip at infim.ro <mailto:lucian.filip at infim.ro>
>> Website: http://lucianfilip.wordpress.com
>>
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>
> _______________________________________________
> The Quantum ESPRESSO community stands by the Ukrainian
> people and expresses its concerns about the devastating
> effects that the Russian military offensive has on their
> country and on the free and peaceful scientific, cultural,
> and economic cooperation amongst peoples
> _______________________________________________
> Quantum ESPRESSO is supported by MaX (www.max-centre.eu)
> users mailing listusers at lists.quantum-espresso.org
> https://lists.quantum-espresso.org/mailman/listinfo/users

-- 
Dr. Lucian Dragos Filip
National Institute of Materials Physics
Atomistilor str. 405A
PO Box MG. 7
Magurele, 077125
Bucharest, Romania
E-mail:lucian.filip at infim.ro
Website:http://lucianfilip.wordpress.com
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