[CPMD-list] no changes in trajectory

[Axel Kohlmeyer]

>>> "YA" == Younes Ansari <ara_1357_2416 at yahoo.com> writes:

YA> Dear CPMD-list :

YA>     I trying to study the interactions of Cs slab which is contain 22 (BCC) atoms of Cs.

YA>      Cs atoms at 301.15 K make a liquid phase and must behave like a liquid, but when I   do a CP calculation and visualize it with VMD atoms just shake in there symmetry position and dose not move.

YA>    So I tried to use the term TEMPERATURE ELECTRON at the same degree with TEMPERATURE but after 9:00 hours I just got same results. I want to know how I can move atoms in a box of 22 Cs in bcc net.      


dear younes ansari,

please check the documentation more closely and have a look at the
output of your simulation (or the ENERGIES files). as pointed out
earlier TEMPERATURE ELECTRON is only useful for FREE ENERGY FUNCTIONAL
calculations and sets the degree of 'smearing' of the bands.

in fact, for a meaningful car-parrinello MD you want to have
the _fictitious_ kinetic energy of the electrons to be almost zero.

now, if you use the keyword TEMPERATURE, this will only set
the _initial_ temperature of your system. since your atoms
will move out of the equilibrium position, kinetic energy
will be converted to potential energy and your instantaneous
temperature will be significantly lower after a while. check
your output. 
to get the desired temperature you'll have to use some thermostatting scheme.
during equilibration, this is most easily done by using TEMPCONTROL
IONS, during production runs (i.e. once your md has reached
equilibrium), you either turn it off or use NOSE IONS.
this is demonstrated with some examples at:
ttp://www.theochem.ruhr-uni-bochum.de/~axel.kohlmeyer/cpmd-tutor/part6.html

also you should be aware of the fact, that with most liquids you have
librational modes in addition to the changes of position and that
due to the small system size you may need a much higher temperature
to 'melt' a crystal. please be also aware, that you are working
under constant volume conditions. this problem also arises for
classical MD and there is a ton of literature available.

please also note (as has been pointed out to you previously, too),
that you _must_ start a regular car-parrinello MD from a previously
calculated (i.e. optimized) wavefunction using RESTART.

final question: why do you have to use NOGEOCHECK ?
if the geometry check prints an error, it is almost
always for a very good reason.

best regards,
     axel

YA> &CPMD

YA>   MOLECULAR DYNAMICS CP

YA>   NOGEOCHECK

YA>   TRAJECTORY XYZ

YA>   TEMPERATURE

YA>    301.5

YA>   TEMPERATURE ELECTRON

YA>    301.5

YA>   ALEXANDER MIXING

YA>    0.9

YA>   MAXSTEP

YA>    1000

YA> &END

YA> &SYSTEM

YA>   SYMMTRY

YA>    1

YA>   CELL

YA>    10.000     1.0    1.0    0.0    0.0    0.0

YA>   CUTOFF

YA>    70

YA>   ANGSTROM

YA> &END

YA> .

YA> .

YA> .

YA> .

 


		
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--

=======================================================================
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.