CLUSTER_DIAMETER
This is part of the adjmat module
It is only available if you configure PLUMED with ./configure –enable-modules=adjmat . Furthermore, this feature is still being developed so take care when using it and report any problems on the mailing list.

Print out the diameter of one of the connected components

As discussed in the section of the manual on Exploiting contact matrices a useful tool for developing complex collective variables is the notion of the so called adjacency matrix. An adjacency matrix is an \(N \times N\) matrix in which the \(i\)th, \(j\)th element tells you whether or not the \(i\)th and \(j\)th atoms/molecules from a set of \(N\) atoms/molecules are adjacent or not. When analyzing these matrix we can treat them as a graph and find connected components using some clustering algorithm. This action is used in tandem with this form of analysis to output the largest of the distances between the pairs of atoms that are connected together in a particular connected component. It is important to note that the quantity that is output by this action cannot be differentiated. As such it cannot be used as a collective variable in a biased simulation.

Compulsory keywords
CLUSTERS the label of the action that does the clustering
CLUSTER ( default=1 ) which cluster would you like to look at 1 is the largest cluster, 2 is the second largest, 3 is the the third largest and so on.
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 input uses PLUMED to calculate a adjacency matrix that connects a pair of atoms if they both have a coordination number that is greater than 2.0 and if they are within 6.0 nm of each other. Depth first search clustering is used to find the connected components in this matrix. The distance between every pair of atoms that are within the largest of the clusters found is then calculated and the largest of these distances is output to a file named colvar.

# Calculate coordination numbers
c1: COORDINATIONNUMBER SPECIES=1-512 SWITCH={EXP D_0=4.0 R_0=0.5 D_MAX=6.0}
# Select coordination numbers that are more than 2.0
cf: MFILTER_MORE DATA=c1 SWITCH={RATIONAL D_0=2.0 R_0=0.1} LOWMEM
# Build a contact matrix
mat: CONTACT_MATRIX ATOMS=cf SWITCH={EXP D_0=4.0 R_0=0.5 D_MAX=6.0}
# Find largest cluster
dfs: DFSCLUSTERING MATRIX=mat
clust1: CLUSTER_PROPERTIES CLUSTERS=dfs CLUSTER=1
dia: CLUSTER_DIAMETER CLUSTERS=dfs CLUSTER=1
PRINT ARG=dia FILE=colvar