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

[Michal Krompiec]

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
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> --
> Oleksandr Motornyi
> PhD candidate
>
> Laboratoire de Solides Irradies
> Ecole Polytechnique (Palaiseau, France)
>
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