[Octopus-users] orthogonalization in td

[matthieu verstraete]

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



-- 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Prof. Matthieu Verstraete

Universite de Liège
Institut de Physique, Bat. B5, 3/7
Allée du 6 aout, 17
B- 4000 Sart Tilman, Liège
Belgium

Associate member European Theoretical Spectroscopy Facility (ETSF
http://www.etsf.eu)

Phone : +32 4 366 90 17
Fax   : +32 4 366 36 29

Mail : matthieu.verstraete at ulg.ac.be
          matthieu.jean.verstraete at gmail.com