How to set CHARMM to run with any size system There are two ways to change the run-time size of charmm arrays to accomodate a system of any size: from command line, and from the charmm input (input file or standard input). Currently only the maximum number of atoms can be set, and other sizes like maximum number of residues, bonds, angles, segments, and so on, are set by an approximation based on number of atoms specified. Command line: $ charmm -chsize nnnnnnnn where nnnnnnnn is the maximum number of atoms in your system, for instance 200000. Input file: Use the charmm command dimension (only dime needs to be specified) immediately after the title: * title dimension chsize 200000 In addition to the overall size, the DIMENSION command can also be used to set the sizes of specific subarrays in the following list: Data Structure Size chsize This is a master size that proportions all CHARMM data structures maxai (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 Example: * title dimension maxa 10000 maxp 10 maximp 10