From: Thomas Cheatham <>
Date: Thu, 8 Jun 2006 18:34:03 -0600 (Mountain Standard Time)

> can somebody tell me why is it that for periodic
> system, only
> the translational COM motion will be removed? unlike
> for non-periodic system, both translational and
> rotational motions are removed after every NSCM steps.

Removing the net translational motion of the box is easily defined;
however, removal of the rotation is not, as it adds a net-torque to the
overall system. Another way to think about it; how can an individual box
rotate within the infinite periodic cell (and if it is an isolated
molecule in vacuo in a periodic cell rotating, as you remove the rotation
motion of the main molecule, you implicitly remove the rotation of all the
periodic images). In practice, some groups have removed this rotational
motion and the artifacts (likely minor) have not been quantified.
Removal of rotation is not necessary; it is expected that the molecule
will rotate... [Removal od translation is necessary since there is no
coupling of this degree of freedom back into the system.]

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Received on Sun Jun 11 2006 - 06:07:15 PDT
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