The new configurable size of CHARMM uses the modified memory management system implemented in CHARMM with the c36b1 release. This allows the general size of CHARMM to be configured with a command line argument (-chsize <size>, see usage.doc), where the size provides the maximum number of atoms and with a default scaling the size of other key arrays and data structures in CHARMM. Alternately, users can configure the size of individual CHARMM arrays at run time as the first command in their CHARMM input script (see usage.doc).

NOTE: usage.doc is not yet updated to document the CHARMM script resizing of CHARMM data structures and arrays. The document component needed is as follows:

Configuring CHARMM Array Sizes in the CHARMM script

The current release of CHARMM (c36b1 and beyond) allows the user to configure the 
size of many key arrays in CHARMM at run-time using a CHARMM script level command
as the FIRST command following the script title. Like the command line option 
-chsize , the script level commands let you configure CHARMM's key arrays 
and data structures to match the problem you are working on. The command key for 
resizing CHARMM arrays is DIMEnsion or RESIze, both are recognized, followed by 
the particular data structure size you wish to change. The command is of the form:

 dimension dsize-1  [dsize-2  ...]

or
 resize dsize-1  [dsize-2  ...]

where the following data structure size names are recognized

Data Structure Size

 chsize            This is a master size that proportions all CHARMM 
                   data structures
 maxa (chsize)     This controls the maximum number of atoms
 maxb (chsize)     Maximum number of bonds
 maxt (chsize*2)   Maximum number of angles
 maxp (chsize*3)   Maximum number of proper dihedral angles
 maximp (chsize/2) Maximum number of improper dihedral angles
 maxnb (chsize/4)  Maximum number of nonbond fixes
 maxpad (chsize)   Maximum number of acceptors and donors
 maxres (chsize/3) Maximum number of residues
 maxseg (chsize/8) Maximum numebr of segments
 maxcrt (chsize/3) Maximum number of CMAP dihedrals
 maxshk (chsize)   Maximum number of SHAKE constraints
 maxaim (chsize*2) Maximum number of atoms including images
 maxgrp (chsize*2/3) Maximum number of groups

EXAMPLES:

   1) Configure all of CHARMM to accommodate 10,000 atoms

      dimension chsize 10000

   2) Configure the maximum number of atoms to be 10,000 and the maximum number of
      dihedrals and impropers to be very small (say 10)

      dimension maxa 10000 maxp 10 maximp 10

NOTE: The remaining arrays/data structures will be configured according to the default chsize used in the CHARMM build, e.g., small, medium, large, xlarge, etc.