VMD-L Mailing List

From: Vermaas, Josh (vermaasj_at_msu.edu)
Date: Sat Feb 26 2022 - 11:57:31 CST

See the docs:

https://www.ks.uiuc.edu/Research/vmd/current/ug/node138.html


  * inertia selection [moments] [eigenvals]: Returns the center of mass and the principles axes of inertia for the selected atoms. If moments is set then the moments of inertia tensor are also returned. With option eigenvals the corresponding eigenvalues will be returned, too. If both flags are set then the eigenvalues will be listed after the moments.
So its spitting back 4 lists. First list is the COM, second are the principle axes, third are the moments, and fourth are the eigenvalues.
-Josh

From: <owner-vmd-l_at_ks.uiuc.edu> on behalf of Alessandro Ruda <alessandro.ruda_at_su.se>
Date: Saturday, February 26, 2022 at 12:02 PM
To: "vmd-l_at_ks.uiuc.edu" <vmd-l_at_ks.uiuc.edu>
Subject: vmd-l: command measure inertia


Hello,



can you please explain me the output of the command:



  * measure inertia $sel moments eigenvals

I get this:

-----------------------
{3.9721615314483643 -8.11227798461914 -0.3456442058086395} {{0.43753355741500854 0.7199295163154602 -0.5387633442878723} {0.5724488496780396 0.23904766142368317 0.7843203544616699} {0.6934455633163452 -0.6515809893608093 -0.3075314462184906}} {{3325.921875 0.0 0.0} {1363.7855224609375 3866.033935546875 0.0} {148.9542236328125 -924.222412109375 4272.4775390625}} {5386.5146484375 4099.5068359375 1978.4119873046875}

Guessing symmetry
Pointgroup: C1, rmsd = 0
Elements:
unique= {1 1 1}
-------------------------

As far as I understood the moment of inertia (eigenvalues) are the last three values in the list, i.e. {5386.5146484375 4099.5068359375 1978.4119873046875}.
But for the rest of the values I am not sure what they refer to exactly.

Thank you in advance!

All the best,
Alessandro