[gmx-users] Radius of gyration and moment of inertia (Dallas Warren)

André Farias de Moura moura at ufscar.br
Sun Feb 3 14:54:54 CET 2019

Hi Aishwarya,

besides distances, the only other physical quantities that enter into the
calculation of moments of inertia are the masses of the particles, so
looking only at the apparent radius at VMD is not enough to say anything
about your results.

so either your systems are indeed different and there are significant
differences in the masses of the atoms comprising each one of them or the
two systems comprise the same atoms/masses, but they are distributed in
very different ways in each system, with heavier atoms closer to the center
in one case and farther in the other.

it is up to you to check which case is your case.


On Tue, Jan 29, 2019 at 8:53 AM Aishwarya Dhar <dhar.aishwarya at gmail.com>

> Hi,
> Yes of course the ratios are similar. The shapes are similar
> But when I measure the distance of the two agrregates in VMD , the length
> of the aggregates and the width of the aggregates are more or less of the
> same dimensions.  Which means that the size of the aggregates are
> comparable and there is no difference in size. So the Ix Iy Iz values
> should be comparable in both the aggregate and not 4x times different.I
> want to know why the the Ix Iy Iz values are 4x times different when the
> shape dimensions are similar. The aggregate size is similar.
> Thanks in advance
> Aishwarya
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Prof. Dr. André Farias de Moura
Department of Chemistry
Federal University of São Carlos
São Carlos - Brazil
phone: +55-16-3351-8090

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