[Octopus-users] orthogonalization in td

[Alberto Castro]

> course. Another possible way out is only to update the external
> potential every X time-steps

Actually, this was implemented some time ago, right? Was it removed at
some point? I can't remember why...

Alberto.

or, even better, only after the ions have
> moved more than a certain distance. This is very easy to implement and
> may speed-up your calculations considerably, as the ions move very
> slowly when compared to the electrons. Of course, there might be issues
> with energy conservation...
>
>  On a side note, it is not stupid at all to calculate vibrational
> spectrum from TDDFT. Actually, you should really take a look at the fast
> Ehrenfest stuff of Xavier et al, that basically allows you to perform a
> "TDDFT" calculation with a larger time-step.
>
>  hope this helped,
>  Miguel
>
> matthieu verstraete wrote:
>> Hello everyone,
>>
>> I am trying a very long td run for a small molecule, to get
>> vibrational spectra from tddft (I know this is not the efficient way
>> to go, it's more for educational purposes). In practice, I need a
>> timestep of 0.01 or 0.001, which makes for horribly long simulations
>> if I want the slow phonon modes to integrate well. I have tried
>> parallelization (8, 16, or 60 procs), but this makes little difference
>> on average (most steps are faster, and a few are much slower, the
>> average is even slightly worse in parallel wrt sequential).
>>
>> In the purely electronic dynamics case (no moving ions and par_domains
>> only) the speedup is brilliant, almost linear. So what can I do? Are
>> things slowed because of an added orthonormalization step or something
>> like that? Can I use some modified Ehrenfest (for the moment it's
>> normal) to improve my time step? My energy is constant for slightly
>> larger dt, but I also need the long time stability in this case, for
>> the low w phonons, so it gets delicate.
>>
>> Cheers
>>
>> Matthieu
>>
>>
>>
>
>
> --
> Dr. Miguel A. L. Marques
> marques at tddft.org
>
> Laboratoire de Physique de la Matière Condensée et Nanostructures
> (LPMCN) - Université Lyon I
> Bâtiment Brillouin, Domaine scientifique de la DOUA
> 69622 Villeurbanne Cedex
> Tel +33 (0)4 72448187
> Fax +33 (0)4 72432648
> _______________________________________________
> Octopus-users mailing list
> Octopus-users at tddft.org
> http://www.tddft.org/mailman/listinfo/octopus-users
>



-- 
===============================
Dr. Alberto Castro

Instituto de Biocomputación y Física de Sistemas Complejos (BIFI),
Corona de Aragón 42,
50009 Zaragoza, España.

Temporarily at:

Departamento de Física Teórica, Facultad de Ciencias,
Universidad de Zaragoza,
Pedro Cerbuna 12,
50009 Zaragoza, España.

Tel:   +34 976761000 3332
Fax:  +34 976761264
skype: alberto_c_barrigon
email: acastro at bifi.es
===============================