   DIHCOR
 This is part of the multicolvar module

Measures the degree of similarity between dihedral angles.

This colvar calculates the following quantity.

$s = \frac{1}{2} \sum_i \left[ 1 + \cos( \phi_i - \psi_i ) \right]$

where the $$\phi_i$$ and $$\psi$$ values and the instantaneous values for the TORSION angles of interest.

The atoms involved can be specified using
 ATOMS the atoms involved in each of the dihedral correlation values you wish to calculate. Keywords like ATOMS1, ATOMS2, ATOMS3,... should be listed and one dihedral correlation will be calculated for each ATOM keyword you specify (all ATOM keywords should specify the indices of 8 atoms). The eventual number of quantities calculated by this action will depend on what functions of the distribution you choose to calculate. You can use multiple instances of this keyword i.e. ATOMS1, ATOMS2, ATOMS3...
Options
 NUMERICAL_DERIVATIVES ( default=off ) calculate the derivatives for these quantities numerically NOPBC ( default=off ) ignore the periodic boundary conditions when calculating distances SERIAL ( default=off ) do the calculation in serial. Do not use MPI LOWMEM ( default=off ) lower the memory requirements TIMINGS ( default=off ) output information on the timings of the various parts of the calculation
Examples

The following provides an example input for the DIHCOR action

DIHCOR ...
ATOMS1=1,2,3,4,5,6,7,8
ATOMS2=5,6,7,8,9,10,11,12
LABEL=dih
... DIHCOR
PRINT ARG=dih FILE=colvar STRIDE=10


In the above input we are calculating the correlation between the torsion angle involving atoms 1, 2, 3 and 4 and the torsion angle involving atoms 5, 6, 7 and 8. This is then added to the correlation between the torsion angle involving atoms 5, 6, 7 and 8 and the correlation angle involving atoms 9, 10, 11 and 12.

Writing out the atoms involved in all the torsion angles in this way can be rather tedious. Thankfully if you are working with protein you can avoid this by using the MOLINFO command. PLUMED uses the pdb file that you provide to this command to learn about the topology of the protein molecule. This means that you can specify torsion angles using the following syntax:

#SETTINGS MOLFILE=regtest/basic/rt32/helix.pdb
MOLINFO MOLTYPE=protein STRUCTURE=myprotein.pdb
dih: DIHCOR ...
ATOMS1=@phi-3,@psi-3
ATOMS2=@psi-3,@phi-4
ATOMS3=@phi-4,@psi-4
...
PRINT ARG=dih FILE=colvar STRIDE=10


Here, @phi-3 tells plumed that you would like to calculate the $$\phi$$ angle in the third residue of the protein. Similarly @psi-4 tells plumed that you want to calculate the $$\psi$$ angle of the fourth residue of the protein.