allows the user to define the system to be studied: in one mode, the
data are retrieved from specified databases; in another mode the data
are read from a previously created file. Finally the command may also
be used to identify experimental data files to be used during
optimisation. When a database search has been performed the data for
the system under study are written to a user-defined or system default
<first database on the database menu>
experiment = <"def.ass">
data = "proj403" !
system = "C, H, O" source = sgte mydata !
data = default !
system = "Al2O3, CaO, SiO2" !
system = "Al, H, Cl" output = "mydata" !
system = "Al, Si" source = "mt-aldata" !
define data = "cumg" experiment = "cumg.ass" !
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 ASSESSMENT, MULTIPHASE, ACCESS, BINARY
If DATA = DEFAULT is used, then the data are read from the last
datafile generated with the default name.
takes the value
specifies the root for a number of
files which may be created and used during subsequent calculations:
a) a single file with
the extension ".mpi"
to which the data resulting from the database search are to be
b) a single file with
to which certain ASSESSMENT diagnostic information
be written, and
If a system is to be
defined this parameter should
be used in the same DEFINE statement that contains the SYSTEM
specification. Use on its own at any other time will automatically
load in data from the default data input file ("def.mpi").
If no output file root is defined then the data are written to
a results file whose name is based upon the root of the data input
takes the value <"component
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.
The best choice of components will depend on the models used to
represent the thermodynamic data. Details as to how components
may be specified can be found in the information about the ACCESS
DEFINE SYSTEM causes
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.
takes the values ALL/ <database
list>/ <"database path">/NONE_BUT<database
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.
a user-defined list
consisting of any of the databases
appearing in the database menu.
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
clears any previous
list and defines a new one.
EXPERIMENT takes the value <"filename">/ default
is the name of a file which contains experimental data. During
subsequent optimisation runs chosen thermodynamic parameters from the
specifed datafile (.mpi file) will be altered to reproduce these
experimental data as closely as possible. During each optimisation run
thermodynamic parameters flagged using the MODIFY INDEX and MODIFY TYPE
commands will be altered automatically to reproduce the experimental
data provided as closely as possible.
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. ASSESSMENT is configured
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
of the UTILITY module. If the number of substances
than can be supported by the ASSESSMENT module it
practice to use the ACCESS module to perform a
screening of species, and write a reduced substance list to a
file. This may then be read by the ASSESSMENT
the DEFINE DATA command.
Another problem that
arises from the database searches
is that of duplicate data sets. A search of the first database
on the list will probably locate the majority of datasets generated
from the list of components defined by the SYSTEM. Substances
located in this way for the first time are added to the MULTIPHASE
DATAFILE and flagged as NORMAL - i.e. present. The search of the
next database on the list will locate data sets of two types:
(a) those for
substances that have been located for
the first time. Data for these substances are written to the file
and flagged as NORMAL - as before.
(b) those for
substances that have already been located
in the search of the first database. Data for these substances
are not written to the file.
The same strategy
applies to interaction between
substances. This strategy of writing data sets to the file only
for those substances that are located for the first time, ie those
that have been classified as NORMAL, means that very few data
from databases low in the database list will be retrieved. If
you wish to select datasets for substances on an individual, rather
than on a first-found basis, then again you should use the ACCESS
module to produce the datafile which can be read in via the DEFINE
A relationship exists
between ACCESS and ASSESSMENT
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 ASSESSMENT and other MTDATA
The recommended method for terminating an ACCESS
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 ASSESSMENT.
If such a filename has not
been defined within
the ACCESS module when the SAVE command is issued,
data are SAVEd to a default file. These data can be retrieved
in ASSESSMENT by the command:
This procedure is to
be recommended only if the ACCESS
and ASSESSMENT modules are used subsequently within
same session of MTDATA. Otherwise, the default
is in danger of being overwritten.