[gmx-users] Dihedral pca

[pratibha kapoor]

Hi,

I would like to carry out dihedral pca with the dihedral angles (phi and
psi) of the peptide backbone. My question is how should I select my
dihedral angles?
I am using
mk_angndx -s *.tpr -n angle.ndx
The angle.ndx file so created contains all the dihedral angles I guess. How
should I select only the phi, psi dihedrals of peptide backbone?
Also,  I am not able to understand the meaning of
[ Phi=180.0_2_33.50 ]
etc. terms in the index file.
Please guide me in proceeding further.

Thanks