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.

Examples

The following provides an example input for the DIHCOR action

Click on the labels of the actions for more information on what each action computes
tested on master
dih: DIHCOR ...
   
ATOMS1
the atoms involved in each of the dihedral correlation values you wish to calculate.
=1,2,3,4,5,6,7,8
ATOMS2
the atoms involved in each of the dihedral correlation values you wish to calculate.
=5,6,7,8,9,10,11,12 ... PRINT
ARG
the input for this action is the scalar output from one or more other actions.
=dih
FILE
the name of the file on which to output these quantities
=colvar
STRIDE
compulsory keyword ( default=1 ) the frequency with which the quantities of interest should be output
=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:

Click on the labels of the actions for more information on what each action computes
tested on master
#SETTINGS MOLFILE=regtest/basic/rt32/helix.pdb
MOLINFO 
MOLTYPE
compulsory keyword ( default=protein ) what kind of molecule is contained in the pdb file - usually not needed since protein/RNA/DNA are compatible
=protein
STRUCTURE
compulsory keyword a file in pdb format containing a reference structure.
=myprotein.pdb dih: DIHCOR ...
ATOMS1
the atoms involved in each of the dihedral correlation values you wish to calculate.
=@phi-3,@psi-3
ATOMS2
the atoms involved in each of the dihedral correlation values you wish to calculate.
=@psi-3,@phi-4
ATOMS3
the atoms involved in each of the dihedral correlation values you wish to calculate.
=@phi-4,@psi-4 ... PRINT
ARG
the input for this action is the scalar output from one or more other actions.
=dih
FILE
the name of the file on which to output these quantities
=colvar
STRIDE
compulsory keyword ( default=1 ) the frequency with which the quantities of interest should be output
=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.

Glossary of keywords and components
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