View source for M03 Equilibrium Lattice Constant and Bulk Modulus

== Reading a Log File ==
In the example scripts of Manual 02, the command '''setnolog''' was activated and
the simulation results were printed out to the standard output, which is usually
your terminal screen. If you want to keep the record of this information, you
comment out the '''setnolog''' command by adding # before it. This
will create a log ﬁle '''A.log''' in the directory speciﬁed by '''dirname'''. For example,
if you run '''mo.script''' in Manual 02 with '''setnolog''' commented out,
then you will ﬁnd a '''A.log''' ﬁle in the '''runs/mo-example''' directory. To read
this ﬁle, type

 $ more runs/mo-example/A.log

In the log ﬁle, the line starting with '''ASSIGN''' shows that a variable 
is assigned to the values as speciﬁed in the script ﬁle. The line with '''EXEC'''
shows the execution of certain command. After the '''eval''' command is executed,
properties such as number of atoms ('''NP'''), potential energy ('''EPOT'''), kinetic
energy ('''KATOM'''), pressure ('''PRESSURE''') and stress ('''Stress''') are also printed.
Sometimes, the log ﬁle may be zipped as '''A.log.gz''', in which case you can use

 $ gzip -cd runs/mo-example/A.log.gz | more

to see the content. To search for a speciﬁc property (''e.g.'' '''EPOT''') in the log
ﬁle, you may use

 $ grep EPOT runs/mo-example/A.log

or

 $ gzip -cd runs/mo-example/A.log.gz | grep EPOT

depending on whether the log ﬁle is zipped or not. In case you want to “grep” several
lines before and after your keyword (''e.g.'' '''Stress'''), you can use

 $ grep -3 Stress runs/mo-example/A.log

This will show three lines above and below any line containing the keyword
“Stress”.

Obviously, this way of extracting the values of MD++ variables is very tedious.  There is a better way to do this, which is to use the Tcl scripting language, as described in [[M08_MD++_Powered_by_Tcl_Language |Manual 08 (will be available soon)]].  The Tcl script for MD++ calculations described in this section is attaced at the end of this manual.