# dimens (c42b1)

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

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