CHARMM Development Project Forums User Discussion & Questions Energy terms, Constraints, Restraints, and Solvation Define selection of atoms with WMAIN

Hi!

I would like to add weighting to selection of the atoms, but I am not sure how to do it.

I have tried with:

define fit sele .byres. prop wmain .eq. 1 .and. .not. hydrogen end

define fit sele .byres. (prop wmain .eq. 1 .and. .not. hydrogen) end

define fit sele (.byres. (prop wmain .eq. 1 )) .and. .not. hydrogen end

But none of the atoms have been selected.

Thank you

These are all syntactically correct.

Do you have heavy atoms with 1(exactly) in the WMAIN array?
You can check with:
SCALar WMAIN SHOW SELECT .NOT. HYDROGEN END

If you suspect a rounding error you can try with .AE. instead of .EQ. in you selection.

Dear Lennart,

it was not exactly 1 so I suppose that is why it could not be read.

What I would also like to understand what does WMAIN column precisely represents and how is it obtained? I have never used it before.

Thanks

I think it could be read, but the values were not equal to 1...

WMAIN is used for a variety of things. When you read a PDB file the B-factors are read into WMAIN. Several CHARMM commands put results in WMAIN or use WMAIN as a weighting array (this is then mentioned in the documentation); the user can access it e.g. using SCALar commands.