[QE-users] safe to enable "k-point algorithm" in turbo_lanczos?

Wed Apr 15 23:59:41 CEST 2020

Dear Iurii
The "TDDFT-solid state affair" seems to periodically resurface from  
deep waters... Most of it started (at least for me) from a 2008 paper  
by Izmaylov&Scuseria (J. Chem. Phys. 2008, 129, 034101) in which some  
assumptions on the usage of range-separated functionals such as HSE  
were made on the grounds of theory and of a (cumbersome...) example of  
an H chain. There is now a vast literature on the tailoring of  
appropriated range-separated hybrid functionals for solid-state TDDFT,  
because we are stubborn and do not basically cope with the fact that  
you can do (almost) whatever you want with TDDFT in the case of 0D  
system, and that all these wonderful things are reduced to some sort  
of poor "joint density of states" in the case of 3D systems! :-D

I would be very happy to read a comment from you: after years of  
painful applications of EXX to QE calculations, which I've pioneered,  
with ACE and ecutfock we have now found a very honorable balance  
between speed and accuracy of ground state calculations (with NC PPs,  
in my experience, but this is another matter). The quest for a  
possible missing rung of the Jacob's excited-state ladder between  
epsilon.x and GW-BSE might be at hand. Thus:

1) Do you think that further effort in the implementation of k_points  
coupled with range-reparated (or even optimally-tuned-like) xc  
functionals working with ACE and ecutfock in turbo_lanczos/davidson  
might provide such a valuable tool?

2) Do you think that such kind of calculation might show (after a lot  
of work, admittedly) a speedup, with respect to a GW-BSE calculation  
of the same system, so spectacular that the juice is worth the squeeze?

Thanks in advance to you and to everybody for any feedback
Giuseppe

Quoting Timrov Iurii <iurii.timrov at epfl.ch>:

> Dear Michal,
>
>
>> @Iurii: the motivation (or rather - hope) is that TDDFT (or
>> perhaps even epsilon.x) will give us the correct trend, whilst being
>> much cheaper than GW/BSE (which we are trying as well).
>
>
> You can try to use the turboEELS code with a very small transferred  
> momentum q. The code prints at the end the loss function  
> -Im[1/eps(w,q)] but also Im[eps(w,q)]. In the long wavelength limit  
> Im[eps(w,q->0)] gives you the optical absorption spectrum at the  
> TDDFT level in the adiabatic approximation with a LDA/GGA functional  
> (see e.g. Fig. 3 in Comput. Phys. Commun. 196, 460 (2015)).
>
>
> Best,
>
> Iurii
>
>
> --
> Dr. Iurii Timrov
> Postdoctoral Researcher
> STI - IMX - THEOS and NCCR - MARVEL
> Swiss Federal Institute of Technology Lausanne (EPFL)
> CH-1015 Lausanne, Switzerland
> +41 21 69 34 881
> http://people.epfl.ch/265334
> ________________________________
> From: users <users-bounces at lists.quantum-espresso.org> on behalf of  
> Michal Krompiec <michal.krompiec at gmail.com>
> Sent: Wednesday, April 15, 2020 7:54:32 PM
> To: Quantum ESPRESSO users Forum
> Subject: Re: [QE-users] safe to enable "k-point algorithm" in turbo_lanczos?
>
> Dear Oleksandr, Dear Iurii,
> Thank you very much, I understand that this code should rather stay
> disabled. @Iurii: the motivation (or rather - hope) is that TDDFT (or
> perhaps even epsilon.x) will give us the correct trend, whilst being
> much cheaper than GW/BSE (which we are trying as well).
> Best,
> Michal
>
> On Wed, 15 Apr 2020 at 18:39, Oleksandr Motornyi
> <oleksandr.motornyi at polytechnique.edu> wrote:
>>
>> Dear Michal,
>>
>>
>> The k-points algorithm of turbo_lanczos.x as it is does not give  
>> the correct results if there is more than one single k-point.  
>> However you can look up the Lanczos implementation in the thermo_pw  
>> module, which works fine with k-points as far as I remember (of  
>> course bare in mind what Iurii said about Adiabatic TDDFT).
>>
>>
>> Regards,
>>
>> Oleksandr
>>
>> On 15/04/2020 19:35, Timrov Iurii wrote:
>>
>> Dear Michal,
>>
>>
>> The k-points implementation of turbo_lanczos.x was not tested and  
>> hence it is disabled. But most importantly, very likely there are  
>> bugs (I think I know a few). Someone has to work on it and fix  
>> bugs. But is there a motivation to do so? Adiabatic TDDFT with  
>> LDA/GGA is known to be not accurate for the optical absorption  
>> spectroscopy of solids.
>>
>>
>> Greetings,
>>
>> Iurii
>>
>>
>> --
>> Dr. Iurii Timrov
>> Postdoctoral Researcher
>> STI - IMX - THEOS and NCCR - MARVEL
>> Swiss Federal Institute of Technology Lausanne (EPFL)
>> CH-1015 Lausanne, Switzerland
>> +41 21 69 34 881
>> http://people.epfl.ch/265334
>> ________________________________
>> From: users <users-bounces at lists.quantum-espresso.org> on behalf of  
>> Michal Krompiec <michal.krompiec at gmail.com>
>> Sent: Wednesday, April 15, 2020 7:26:09 PM
>> To: Quantum Espresso users Forum
>> Subject: [QE-users] safe to enable "k-point algorithm" in turbo_lanczos?
>>
>> Hello,
>> I'm trying to compute the spectrum of a crystalline insulator using
>> turbo_lanczos. I got the following error:
>>
>>      Error in routine lr_readin (1):
>>      k-point algorithm is not tested yet
>>
>>
>>
>> I guess I could just comment line 477 out in TDDFPT/src/lr_readin.f90
>> to disable this error:
>>
>>        ! K-points are implemented but still unsupported (use at  
>> your own risk!)
>>        !
>>        IF (.NOT. gamma_only ) CALL errore('lr_readin', 'k-point
>> algorithm is not tested yet',1)
>>
>> But how unstable is this code? Any reason not to try this?
>>
>> Thanks,
>>
>> Michal Krompiec
>> Merck KGaA
>> _______________________________________________
>> Quantum ESPRESSO is supported by MaX  
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>> users mailing list users at lists.quantum-espresso.org
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>> _______________________________________________
>> Quantum ESPRESSO is supported by MaX  
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>>
>> --
>> Oleksandr Motornyi
>> PhD candidate
>>
>> Laboratoire de Solides Irradies
>> Ecole Polytechnique (Palaiseau, France)
>>
>> _______________________________________________
>> Quantum ESPRESSO is supported by MaX  
>> (www.max-centre.eu/quantum-espresso<http://www.max-centre.eu/quantum-espresso>)
>> users mailing list users at lists.quantum-espresso.org
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> _______________________________________________
> Quantum ESPRESSO is supported by MaX  
> (www.max-centre.eu/quantum-espresso<http://www.max-centre.eu/quantum-espresso>)
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GIUSEPPE MATTIOLI
CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
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