[CPMD-list] Rotation in Isolated Molecule MD

[Francesco Filippone]

Dear Petr,

in CPMD only cartesian coordinates are used, i.e. the  initialization of 
the velocities in a MD run is not done with any internal  coordinate at 
all. And using cartesian coordinates inevitably means adding  some 
contribution from translations and rotations of the molecule.

In secder.F and phonons_p.F there are two "twin" couples of routines, 
settrans  and setrotat, and settras and setrot that build the "a priori" 
translations and rotations to be used in the vibrational analysis. 
They are basically the same. You can try to use them as starting point 
either to implement a new MD constraint  either to project out these 
degrees of freedom from the TRAJECTORY in the post-processing.

Ciao,
F.

On Thu, 9 May 2002, [iso-8859-2] Petr Kulhánek wrote:

> Dear cpmd users,
> 
> I have some problems with isolated molecule MD. When I start MD the molecule
> always gets rotational moment.I think that this is not right because
> rotational energy cannot be exchange with vibrational one (no colisions
> exist in isolated molecule aproach). Do you have any idea how this
> rotational moment can be removed or at least quantified ?
> Thanks in advance,
> 
> Petr Kulhanek
> 

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