[CPMD-list] butane MD follow-up

[Axel Kohlmeyer]

On Sat, 8 Dec 2007, Bin Pan wrote:

BP> Dear CPMD users,

dear bin pan,

BP>       I also did the MD on a single butane, but starting with two
BP>       different optimized but constrained c1-c2-c3-c4 dihedral
BP>       angles.
BP>       The first one is at potential energy minimum, while the
BP>       second one is at a local maximum in the potential-energy vs.
BP>       dihedral angle.

please note that the following comes out completely unreadable
for everbody who uses (because of volume of e-mail and/or "historical
reasons"m or because of choice) a text mode mail program.

BP>       I got the following output:
BP>       starting from minimum:
BP> 
BP>        []
BP>       []  
BP>       starting from local maximum:
BP> 
BP> []
BP> []
BP> 
BP> 
BP> The second one is obviously wrong. Can you point to me where I did wrong?

instead of an answer, i have a couple of questions:

why do you use a thermostat on the electrons?

have you noticed the _huge_ difference between the electron
thermostat target value and the actual fictitious kinetic energy?

have you noticed, that in the second case, the ficitious kinetic
energy increases steeply at the same time, where your KS and 
classical energy "explodes" as well? what do you think this means?
what are the pre-requisites to do a meaningful CP dynamics run?

since you have a very small system, 
why do you use a thermostat at all?

or more generally asked, what is the purpose of 
your calculations (apart from curiosity, of course)?

BP> The input is as follows(only one):
BP> &CPMD
BP>   MOLECULAR DYNAMICS
BP>   RESTART WAVEFUNCTION COORDINATES VELOCITIES GEOFILE
BP>   MAXSTEP
BP>   20000
BP>   TIMESTEP
BP>    4
BP>   EMASS
BP>    400.
BP>   QNENCH BO

check your output. ist this properly recognized or
an intentional spelling error (to disable the flag).

generally for a setup like yours, it may be safer to use
QUENCH BO ELECTRONS, to make sure that your fictitious
kinetic energy is properly reset.

cheers,
   axel.

BP>   TEMPERATURE
BP>     300.
BP>  NOSE IONS
BP>     300.0  4000.0
BP>  NOSE ELECTRONS
BP>     0.001  10000.0
BP>   TRAJECTORY SAMPLE
BP>    1
BP>   STORE
BP>    200

[...]

-- 
=======================================================================
Axel Kohlmeyer   akohlmey at cmm.chem.upenn.edu   http://www.cmm.upenn.edu
   Center for Molecular Modeling   --   University of Pennsylvania
Department of Chemistry, 231 S.34th Street, Philadelphia, PA 19104-6323
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