Basic Usage

CHARMM remains essentially a command line program that is typically run on Unix computers.

The general syntax for using the program (assuming /bin/csh) is:

charmm < file.inp >& file.out [[param:value] ...] [ & ] 

The input file file.inp is a text file containing CHARMM input commands, using the command syntax described below. In the example, output from CHARMM is written to file.out. Additional parameters can be passed to CHARMM via param:value command line arguments that can be accessed via @param within the input script.

For parallel usage, the command to run CHARMM is more complex, and depends on the both the parallel library (typically an MPI implementation), and local conventions at the computing facility. A typical example command using mpirun may look like this:

mpirun -n 64 charmm-mpi -i file.inp >& file.out

How to use CHARMM The user of CHARMM controls its execution by executing commands sequentially from a command file or interactivly. In general the ordering of commands is limited only by the data required by the command. For example, the energy cannot be calculated unless the arrays holding the coordinates, the parameters, etc., have already been filled. This section deals with overall usage, as opposed to the detailed description of any given command. This is a good place to start when first learning CHARMM. * Starting CHARMM / Unix command line arguments * CHARMM Size / Configuring CHARMM size from a CHARMM script * Meta-Syntax / Describing the Syntax of Charmm Script Commands * Command Syntax / Rules for composing command input files. * Run Control / Ways to modify control flow and stream switching. * I/O Units / Correspondence between files and unit numbers used by CHARMM. * AKMA / Units of Measurement used in CHARMM * Data Structures / Data Structures used by CHARMM * Standard Files / Descriptions of parameters, topologies, and coordinates available. * Examples / Sample runs * Interface / How to make your own private version of CHARMM * Syntactic Glossary / Glossary of syntactic terms * Glossary / Glossary of non-syntactic terms.
Top Starting CHARMM from Unix shell (command line or in a batch script) $ charmm [arguments] [< input] [>output] This command assumes that the charmm command is in your path. If not, give the fully qualified path to charmm. The square-bracketed arguments are optional but almost always used for normal runs. Input and Output: The charmm executable reads input from standard input and writes to standard output by default. The charmm input can be given interactively via the keyboard if no redirect of input is specified. Input can be redirected using "<" from a file but should only be done for non-parallel runs. Output can always be redirected to a file using ">". Alternatively the arguments "-i filename" or "-input filename" can be used to specify an input file, and "-o filename" or "-output filename" can be used to specify an output file. Command line arguments: ARGUMENTS may be specified in any order. Redirection (<, >, or |) must be specified after all arguments. -h, -help - charmm prints allowed command line arguments and quits -chsize N - sets arrays to run for maximum atoms of N, an integer specified by the user here -prevclcg - runs in mode compatible with previous CLCG -prevrandom - runs in old random number generator mode -input file - specifies input file to be read instead of standard input -i file -output file - specifies output file to be used instead of standard output -o file var=value - sets a scripting variable to be used in the charmm script as an "@" variable, the same as the "SET" command (miscom.doc). This argument allows the same charmm script to be used with different values of @ variables without editing the scripts. EXAMPLE: $ charmm runs charmm interactively, all input comes from keyboard, all output comes to screen. $ charmm < myinput.inp or $ charmm -i myinput.inp runs charmm reading input from a file in the present working directory, output to screen or standard output $ charmm < myinput.inp > chmout.out $ charmm -i myinput.inp > chmout.out $ charmm -o chmout.out -i myinput.inp $ charmm -o chmout.out < myinput.inp $ charmm -i myinput.inp -o chmout.out All equivalent, last recommended for parallel runs runs charmm reading input from a file in the present working directory, output to screen or standard output $ charmm aaa=5 rtffile=top_mine.rtf run=$nrun -prevrandom < myinput.inp runs charmm, reads from myinput.inp, writes to standard output. Sets three variables as if the first lines in the charmm script were (where the shell or environment variable nrun is 33): set aaa 5 set rtffile top_mine.rtf set run 33 $ charmm -chsize 500000 -input myinput.inp runs charmm, reads from myinput.inp, writes to standard output. Sets size of charmm arrays to hold 500,000 atoms as if the first line in the charmm script was: dimension chsize 500000
Top 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 <integer>, 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 <size-1> [dsize-2 <size-2> ...] or resize dsize-1 <size-1> [dsize-2 <size-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 maxnbf (chsize/360) Maximum number of non-bond fixes maxitc (chsize/360) Maximum number of atom type codes 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.
Top Rules for Describing the Syntax (The Meta-Syntax) The syntax of commands is described using the following rules: Capitalized words are keywords that must be specified as is. However, if the word is partially capitalized, it may be abbreviated to the capitalized part. Lower case words are to be replaced by a corresponding data entry. The symbol "::=" means "has the following syntactic form:". Anything enclosed in square brackets, "[]", is optional. If several things are stacked in square brackets, one may choose one optionally. Anything enclosed in curly brackets, "{}", specifies that a selection must be made of the choices stacked vertically inside. The syntactic entities which appear as an argument to "repeat" may be repeated any number (including zero) times. Defaults for optional parameters may be enclosed in apostrophes and placed under the entity they stand for. However, defaults are not specified in this manner if the rules for the default are complex. The syntactic glossary, see *note glossary: Syntactic Glossary, contains further syntactic entities which are used in the command descriptions. Finally, the options and operands in each command can usually be specified in any order except if otherwise noted.
Top Command language rules and lore A CHARMM run is controlled by a command file (or files). This section of the documentation describes the basic rules for the command file. Details of command level run control are described in the next node. A command file for CHARMM should begin with a specification of the title of the run. (See the syntactic glossary, *note syn: syntactic glossary, for the syntax of a title.) Then, any number of commands may be specified. Each command consists of a command line possibly followed by other data. The command line is scanned free field. This command line may be longer than one line in the file; to do this, one must place a hyphen at the end of line which is to be continued on the next line. Comments may be placed on a command line by preceding the comments by exclamation points. All lower case characters are converted to upper case. This format is identical to that used by the VAX command language interpreter. In addition, blank lines are permitted to separate blocks of commands for increased readability. The first word of every command line specifies the command. Generally, required operands of a command must follow in order. On the other hand, options may generally be specified in any order. Further, any number is always preceded by a key word so that any numeric operands, can be placed in arbitrary order. The command line is scanned in units of words and delimited strings. A word is defined by a sequence of non-blank characters, A delimited string consists of a keyword followed by a string of characters of variable length followed by a delimiter string. One example of where a delimeter string is used is in atom selection where the syntax is; SELE ...... END. Note, that the "END" is required and delimits the atom selection. Abbreviations are permitted in various contexts. The first word may be abbreviated to four characters and numerous options and operands may also be abbreviated to four characters. However, some key words which are used to mark numbers may not be abbreviated. See the processing for individual commands to see what can and cannot be abbreviated. Many of the various options and numeric values are maintained from one invocation of a command to the next. Once a value is specified, it is maintained until it is changed in any command. Therefore, if CUTNB is specified in a NBON command, that value will be used in the DYNA command unless it is changed therein. Usually, when a free field command line is read in, it is echoed onto a standard output. Each such echo will be prepended by a short marker, eg. "CHARMM>", which identifies the line of input as well as the command processor which is interpreting it. In general, as each of the command is interpreted, it is deleted from the command line. When command processing is finished, a check is made to see that nothing is left over. The presence of extraneous junk indicates that something was mistyped. For some commands, such as DYNAmics, where a mistake may be costly, extraneous characters result in a fatal error.
Top Controlling a CHARMM Run The sizes of arrays can now be dynamically defined at program startup, instead of having to recompile. The charmm-size (chsize) is no longer limited to the compile time flag of MEDIUM, LARGE, XLARGE, etc., and can be changed either via the command line (see above) or the DIMEnsion command, which **MUST** be the first command in the input file. Otherwise, the compile time limit is used. Other arrays may also be specified; DIMEnsion DIMEsion chsize <number of atoms> ! max number of atoms for this run Control Logic IF command-parameter test-spec comparison-string command-spec GOTO label-string LABEL label-string STREAM [UNIT integer] [file-specification] RETURN SET command-parameter string INCRement command-parameter [BY real] DECRement command-parameter [BY real] *note Miscellaneous commands:(chmdoc/miscom.doc) These commands that are used to modify the usual sequential interpretation of commands from the command file. Three methods are available to accomplish this: IF tests to conditionally execute a single command GOTO and LABEL transfers within a file STREAM and RETURN transfers to different command files. In addition commands can be modified by the use of command parameters. The command line reader scans input lines for parameters (specified by @n where n is an alphanumeric character) and will subsitute the appropriate parameter string. Command parameters are defined using the SET command to set one of the 36 command parameters, and their values (if numeric) can be modified by the INCRement command, which decodes the parameter string, does real arithmetic and encodes the result. The command parameters are identified by alphanumeric characters (0-9,A(a)-Z(z)(not case-sensitive)). IF compares the string in the specified parameter string to the comparison-string using the test-spec (GT GE EQ NE LE LT). If the comparison is true then the rest of the command line is executed (otherwise it is ignored). The EQ and NE comparisons are done as string comparisons, but the others require decoding of the two strings and comparison by real arithmetic. The command-spec can be any valid command line (including another IF test or a GOTO or STREAM specification). GOTO causes the current command file to be rewound and searched for a line containing the correct LABEL and label-string. The label-string is a single word. If multiple occurrences of a label are present, the first will be used. Command interpretation begins on the line following the LABEL (any information after the LABEL keyword and label-string is ignored). STREAM iunit begins reading commands from the specified fortran logical unit or from the stream file. The stream file is treated exactly as the main command file. It begins with a title and ends with a STOP or RETURN, the latter causing control to return to the previously active command file at the point where the stream switch occurred. The logical unit in OPEN, CLOSE, and REWIND commands are useful in working with streams see MISCOM . EXAMPLE: * This is a sample command file for CHARMM which calls a stream file * to build a structure and then maps out an adiabatic potential * surface defined by a pair of dihedrals OPEN UNIT 10 READ FORM NAME makestruc.inp STREAM UNIT 10 SET 1 -180. SET 2 -180. LABEL LOOP CONS CLDH CONS DIHE first-dihedral-angle-spec FORCE 100.0 MIN @1 CONS DIHE second-dihedral-angle-spec FORCE 100.0 MIN @2 MINI minimization-spec INCR 1 BY 30.0 IF 1 LT 170. GOTO LOOP SET 1 -180. INCR 2 BY 30.0 IF 2 LT 170. GOTO LOOP STOP
Top Fortran I/O Units Usage by CHARMM In order to keep CHARMM as machine independent as possible, all specification of files is done through Fortran unit numbers. Two unit numbers have special signifigance, 5 and 6. Unit 5 is the command file interpreted by CHARMM. Unit 6 is the output file for all printed messages. As commands are read from unit 5, they are echoed on unit 6. All other unit numbers have no predefined meaning. The CHARMM OPEN command may be used to assign files to units. The stream file in "STREAM file-specfication" may be assigned to a logical unit between 100 and 119 (80 and 99 on Cray machines). Logical unit 0 through 9 may be used for CHARMM internal file handling. We recommend logical units 10 through 79 for user data files.
Top The CHARMM system of units: AKMA. CHARMM uses a distinct system of units, the AKMA system. I.e. Angstroms, Kilocalories/Mole, Atomic mass units. All distances are measured in Angstroms, energies in kcal/mole, mass in atomic mass units, and charge is in units of electron charge. Using this system, the AMKA unit of time is 4.888821E-14 seconds (based on the constants tabulated in Abramowitz and Stegun (1970)), however, for all input and output, the time is listed in picoseconds (20 AKMA time units is .978 picoseconds). In some places, the users may specify values in AKMA time units, and in some places both picosecond and AKMA time are output. Angles are given in degrees for the analysis and constraint sections. In parameter files, the minimum positions of angles are specified in degrees, but the force constants for angles, dihedrals, and dihedral constraints are specified in kcal/mole/radian/radian. Any numbers used in the documentation may be assumed to be in AKMA units unless otherwise noted.
Top Data Structures You Should Understand There are a number of data structures that CHARMM manipulates. Many of these data structures are important for most operations; others which are less important, are described with the commands that use them. Much more specific information is available in the various common blocks whose extension is .fcm in the source directory, ~/charmm/source/fcm ([...CHARMM.SOURCE.FCM] on VAX). The important data structures are given below: Each data structure name is followed by its abbreviation which is used as its name in commands. 1) Residue Topology File (RTF) The residue topology file stores the definitions of all residues. The atoms, atomic properties, bonds, bond angles, torsion angles, improper torsion angles, hydrogen bond donors and acceptors and antecedents, and non-bonded exclusions are all specified on a per residue basis. The term "residue" is somewhat historical, but can be any basic unit. 2) The Parameters (PARA or PARM) The parameters specify the force constants, equilibrium geometries, van der Waals radii, and other such data needed for calculating the energy. 3) Structure File (PSF) The structure file is the concatenation of information in the RTF. It specifies the information for the entire structure. It has a hierarchical organization wherein atoms are grouped into residues which are grouped into segments which comprise the structure. Each atom is uniquely identified within a residue by its IUPAC name, residue identifier, and its segment identifier. Identifiers may be up to 4 characters in length. 4) The Internal Coordinates (IC) The internal coordinates data structure contains information concerning the relative positions of atoms within a structure. This data structure is most commonly used to build or modify cartesian coordinates from known or desired internal coordinate values. It is also used in conjunction with the analysis of normal modes. Since there are complete editing facilities, it can be used as a simple but powerful method of examining or analyzing structures. 5) The Coordinates (COOR) The coordinates are the Cartesian coordinates for all the atoms in the PSF. There are two sets of coordinates provided. The main set is the default used for all operations involving the positions of the atoms. A comparison set (also called the reference set) is provided for a variety of purposes, such as a reference for rotation or operations which involve differences between coordinates for a particular molecule. Associated with each coordinate set is a general purpose weighting array (one element for each atom). 6) The Non-bonded List (NBON) The non-bonded list contains the list of non-bonded interactions to be used in calculating the energies as well as optional information about the charge, dipole moment, and quadrapole moments of the residues. This data structure depends on the coordinates for its construction and must be periodically updated if the coordinates are being modified. 7) The Hydrogen Bond List (HBON) The hydrogen bond list contains the list of hydrogen bonds. Like the non-bonded list, this data structure depends on the coordinates and must be periodically updated. 8) The Constraints (CONS) There is a variety of available constraints. All data pertaining to constraints reside in this data structure. 9) The Images data structure (IMAGES) The images data structure determines and defines the relative positions and orientations of any symmetric image of the primary molecule(s). The purpose of this data structure is to allow the simulation of crystal symmetry or the use of periodic boundary conditions. Also contined in this data structure is information concerning all nonbonded, H-bonds, and bonded interactions between primary and image atoms.
Top Files available for general use There are number of residue topology files, parameter files, coordinates files and files of other data structures available. The most important files generally available are residue topology and parameter files. Both such classes of files are stored for general use in the CnnPT: directories. The file names used for both these files consists of an alphabetic part followed by a number, e.g. PARAM7. There are two copies of each file; one with extension, .INP, which is a character files used as an command file to generate the binary file, with extension, .MOD. The .INP is meant for human eyes; the .MOD files is meant for CHARMM to read efficiently. The numeric part of each name is its version number. In general, one should use the highest version number of a file. Although parameter files and toplogy files are separate, they are usually associated, and they must be taken together when generating a structure (PSF). For example, a parameter set for proteins will not work with a DNA topology file. For information on the general use of directories, and the files they contain, see the following sections. Parameters / Description of all the parameter files Residue / Description of the topology files (RTF)
Top Sample CHARMM Runs For an example of specification of a CHARMM run, examine a test case in ~/charmm/test. The file, TEST.INP, is an input to The file, TEST.OUT, contains the output from CHARMM produced on Fortran unit 6. Other test cases are found in the test directory. File:Usage, Node: Interface, Up: Top, Next: Syntactic Glossary, Previous:Examples Interfacing to CHARMM A mechanism has been provided to allow users of the incorporated into the system without threatening its integrity. There are six "hooks" into the CHARMM which have been specially provided for casual modifiers. For detailed descriptions of each of these hooks, consult the routine in ~/charmm/source/main/usersb.src 1) USERSB The USER command invokes the subroutine, USERSB, and performs no other action. USERSB is a subroutine with no arguments. However, parameters may be passed to this subroutine via modules. These modules store nearly all of the systems data. These modules should be created in the source directories for the version of the program you are using. 2) USERE A user supplied energy routine may be provided that will be invoked on every energy evaluation. The force arrays should be modified accordingly. 3) USRSEL If one need to be able to select atoms in a manner not possible with the existing options, a user selection routine may be specified. One such example would be for for selecting atoms within a given rectangular solid, or other (nonsperical) solid. 4) USERNM Within VIBRAN, a user specified vector or mode may be generated with this routine. One command that appends this motion onto the existing set of vectors is "EDIT INCL USER integer". 5) USERF A user specified parameter fitting routine may be specified. 6) USRTIM A user specified time series routine may be provied for use in computing correlation functions. #_OLD ???? mfc #_OLD ???? mfc To simplify the use of these hooks and to allow users to replace #_OLD ???? mfc subprograms in the CHARMM with their own versions of said #_OLD ???? mfc subprograms, the command procedure BUILD has been provided. BUILD #_OLD ???? mfc will produce a private version of the CHARMM in your default USER #_OLD ???? mfc directory using your versions of USERSB and USERE. The procedure #_OLD ???? mfc looks in your directory for USERSB.SRC and USERE.SRC. If either file #_OLD ???? mfc (or both) is found, it is used in the make procedure of the CHARMM. #_OLD ???? mfc #_OLD ???? mfc BUILD command should always be used to generate a private #_OLD ???? mfc version of the CHARMM as it will always use the correct files for #_OLD ???? mfc linking. #_OLD ???? mfc Before attempting to write your own USER functions, you should familiarize yourself with the information available onthe implementation of CHARMM. This interface procedure is designed for short, one time programs. If a user written subroutine is of general use, the routine should be rewritten to conform to parameter passing standards used in the system and then will be incorporated into the central CHARMM. There are several utility routines available to a user routine. Some of them are listed below. CALL GETE(X,Y,Z,...) will cause the energy and forces to be computed and values are saved appropriately. For this to work properly, NBONDS, HBONDS, and CODES must have been called. This can be done by executing both the NBONds and HBONds command, by the use of the UPDAte command, or by having previously found the energy (minimization, dynamics, etc..). CALL PRINTE(...) will write the current energy values (from common block values) to the specified unit (IUNIT). It will also write out the cycle or iteration number and optionally write out the standard header. File:Usage, Node:Syntactic Glossary, Up:Top, Next:Glossary, Previous: Interface Glossary of Syntactic Terms char A character del The delimiter - a single character which is used to mark the end of a portion of a command. Initially, it is a dollar sign but can be changed using the DELIM command, see delim . It should be noted that the delimiter cannot be a character within any string it is supposed to delimit. deldel Two delimiters concatened together with no space in between. int or integer An integer iupac IUPAC name for an atom. Initially specified in the residue topology file. keyword A word, see below, serving to identify some option range equivalent to real real integer. The first real is the minimum value in the range, the second number is the maximum value in the range, and the third number gives the number of interval, i.e. lines or columns. real A real number. No decimal point is required for the number to be interpreted correctly resid Residue identifier (a string of upto 4 characters) resname Residue name (type of residue. e.g. GUA) segid Segment identifier (a string of upto 4 characters) string An ordered set of characters tag A string which is a tag, i.e. no embedded spaces. title A series of 1 to 32 lines of text (max 80 characters per line) each starting with a "*". The title is terminated by a line which an asterisk "*" as the first character. Used for commenting files. word A string with no blanks unit-number An integer which is a Fortran unit number.
Top General Glossary data structure A collection of arrays, scalars, and possibly other data structures which are related by part of a larger entity. For example, a coordinate set is a data structure which hold the three dimensional positions of atoms. This data structure consists of 1 scalar and three arrays. The scalar is the number of coordinates; the three arrays are the X, Y, and Z components of the coordinates. Internal bonds, angles, torsions, improper torsions. coordinates Also, a data structure used for constructing coordinates. Iupac Name for The name of an atom with a residue. This name should be an atom unique within a residue and should conform to the IUPAC nomenclature, Biochemistry 9:3471 (1970) Hbonds hydrogen bonds Parameters constants in the energy expression ( force constants, minima of energy surfaces, charges, Lennard-Jones parameters, van der Waals radii, etc.) PSF structure file ( protein structure file ) : a list of the internal coordinates and related information Residue A string of four characters or less which uniquely specifies Identifier residue with in a segment. This value is currently set by CHARMM to be the character representation of the residue number in the segment starting from the first real monomer unit in it. RTF residue topology file : a list of standard internal coordinates, atom charges, atom types, excluded non-bonded interactions, etc. Segment A string of up to four characters uniquely designating Identifier a segment. Specified in the GENErate command, see gener: Generate. Sequence list of residues