MTDATA – Phase Diagram Software from the National Physical Laboratory

 

 

 

Home 

News 

Products 


Training and Support 

FAQs 

Links 

Agents 

Other Services 

 

Services 

 

 

DEFINE

Function:

Allows the user to define the system to be studied: in one mode, the data are retrieved from specified databases; in the alternative mode the data are read from a previously created file. When a database search has been performed the data for the system under study are written to a user-defined or system default file.

Parameters:

data_input_file

output_data/results

system

source

Defaults:

data_input_file = <"def.mpi">

output_data/results = <"def">

source = <first database on the database menu>

Examples:

define data = "project4" !

define system = "Cu, S, /-, O, H"  source = aqe aqd !

define data = default !

define system = "Al, H, Cl, O" output 'myalhclo' !

Parameter values:

DATA_INPUT_FILE takes the values <"filename">/DEFAULT

If the DEFINE statement contains a reference to a DATA_INPUT_FILE the program reads the required data from the specified datafile. Such a datafile could have been created in a previous run of COPLOT, MULTIPHASE or ACCESS. If DATA = DEFAULT is used, then the data are read from the last datafile generated with the default name, usually "def.mpi".

OUTPUT_DATA/RESULTS takes the value <"file root">

This parameter specifies file to which the data resulting from the database search are to be sent. The output file is specified in the same DEFINE statement as that of the SYSTEM specification. If no output file root is defined then the data are written to a system default file, typically "def.mpi" in the current directory. 

OUTPUT_DATA/RESULTS does not change the name of the file that contains the results of COPLOT calculations, which is always called COPOUT.DAT and is overwritten by each new calculations.

SYSTEM takes the value <"component list">

The SYSTEM parameter is used to define the components of the system to be studied prior to the search of one or more databases. Components may be elements, compounds or charged species. For COPLOT a charged species must appear other than last in the list if the system is to be 'open' to charge. 

define system = "Cu,S,/-,H,O" !
define system = "Cu,S,H2O,H/+,O" !

will retrieve the same set of substances. Never include more than one charged somponent in the component list.

DEFINE SYSTEM is executive causing the program to search the list of databases specified by use of the SOURCE parameter, for the substances that are linear combinations of the components DEFINEd. These are written to a datafile based upon the OUTPUT_DATA/RESULTS file root and then loaded into memory.

SOURCE takes the values ALL/ <database list>/ <"database path">/NONE_BUT<database list>

This defines the databases to be searched in the specified order. It is recommended that the SYSTEM and SOURCE parameters are set within the same DEFINE statement. If the SOURCE parameter is assigned a value before a DEFINE SYSTEM command is issued the default data input file is also loaded. If a value for the SOURCE parameter is not specified the first database in the database menu is searched when the SYSTEM is defined. If aqueous water or the aqueous electron is required in the system, it may be necessary to include the AQEXTRAS database in the list.

<database list>

a user-defined list consisting of any of the databases appearing in the database menu.

<"database path">

the path of a database not on the database list.

ALL this specifies the complete list of databases in the order in which they appear in the database menu.

NONE_BUT<database list>

clears any previous list and defines a new one.

General comments:

When the DEFINE SYSTEM command is executed, the databases specified by use of the SOURCE parameter are searched in the specified order for all the substances that are linear combinations of the components defined by the SYSTEM. For a large number of components, the number of substances retrieved may easily run to tens, if not hundreds, of species. COPLOT is configured to deal with at least 200 substances, the actual limits depending on the type of computer being used. The limits for a particular version of MTDATA can be inspected by using the LIMITS command of the UTILITY module. If the number of substances is larger than can be supported by the COPLOT module it is better practice to use the ACCESS module to perform a preliminary screening of species, and write a reduced substance list to a file. This may then be read by the COPLOT module using the DEFINE DATA command.

A relationship exists between ACCESS and COPLOT in terms of the datafiles that are generated. The purpose of using ACCESS is to perform a preliminary review of the data and to enable phases and/or substances to be excluded from the MULTIPHASE input data file created so that it is suitable, in size and form, for use by COPLOT and other MTDATA modules. The recommended method for terminating an ACCESS session is to define the name of a file to which the edited data may be SAVEd and then to issue the SAVE command. At a later date the file may subsequently be read by the DEFINE DATA statement in COPLOT. If such a filename has not been defined within the ACCESS module when the SAVE command is issued, the data are SAVEd to a default file. These data can be retrieved in COPLOT by the command:

define data=default !

This procedure is to be recommended only if the ACCESS and COPLOT modules are used subsequently within the same session of MTDATA. Otherwise, the default datafile is in danger of being overwritten.

 

Updated 6 July 2010