[CPMD-list] problem with time

[Axel Kohlmeyer]

On Sun, 12 Jun 2005, Younes Ansari wrote:

YA> Dear cpmd mailing list:

YA>  I have done wavefunction optimization and geometry optimization for
YA> 54 atoms of cesium but it took 5 days .
YA>  I want to know if it would be possible to do different MDs by the
YA> same condition just by changing the box lenght and temperature with
YA> the same wavefunction optimization and geometry optimization.

dear younes ansari,

you can start molecular dynamics runs with different temperatures
from the same wavefunction. in fact, i would recommend you start
the next temperature in a series from the restart of the previous
ones, so you don't need to waste too much time on equilibration.

how many wavefunction steps did you manage in those 5 days?
and what kind of hardware do you have at your disposal? 

i hope you are aware of the fact, that you need a _serious_ 
amount of computer power for a decent set of MD trajectories.

also, in your input file example there are some issues, 
that you should seriously consider before you start a 
serious study (and waste a lot of CPU time):

1.) you were obviously using a Goedecker pseudopotential
with only the 6s state in the valence. did you check what
kind of plane wave cutoff you need. my guess is, that you
can get away with much less than 70ry for this potential.

2.) Caesium is a metal, and i suspect that a gamma point
calculation is not sufficient. did you check for k-point
convergence? you probably need to use the FREE ENERGY
FUNCTIONAL keyword, too. which will then make the whole
calculation _much_ more expensive.

3.) TEMPCONTROL has no meaning for a geometry optimization.

best regards,
	axel kohlmeyer.

--
=======================================================================
Dr. Axel Kohlmeyer   e-mail: axel.kohlmeyer at theochem.ruhr-uni-bochum.de
Lehrstuhl fuer Theoretische Chemie          Phone: ++49 (0)234/32-26673
Ruhr-Universitaet Bochum - NC 03/53         Fax:   ++49 (0)234/32-14045
D-44780 Bochum  http://www.theochem.ruhr-uni-bochum.de/~axel.kohlmeyer/
=======================================================================
If you make something idiot-proof, the universe creates a better idiot.