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Dear VASP Team,

I was trying to set up an ICONST file for a calculation where I'm trying to set up my collective variable as the distance between a C atom, and the Centre of Mass of 3 atoms (say H atoms). I know that we define primitive coordinate using R flag, and complex coordinates using S flag, however rest of the mentioned flags are for cartesian coordinates and bond centers as such. Is there any way to implement this in ICONST file for a metadynamics simulation in VASP?

Thank you for the help!

Dear Pranav,

Thank you for your question. There is no specific way to define the centre of mass using ICONST.

However, ICONST can be used to define more than two coordinates, so you could define three different primitive coordinates,e.g. the distance between the C atoms and each H atom, then monitor these:

R 3 4 0
R 3 5 0
R 3 6 0
S 1 0 0 7
S 0 1 0 7
S 0 0 1 7

Using your own script, you could calculate the distance to the centre of mass of these atoms. E.g. in my output it gives:

  Monit_coord
   mc> S          1.07090
   mc> S          1.12301
   mc> S          1.05014

Does this answer your question?

Best wishes,

Chris