[lammps-users] two sets of T and P values ?

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1

Hi, ALL

I have just been studying LAMMPS for a couple of days. When reading the online manual, I get confused by the following statement.

“Finally, thermodynamic output, which can be setup via the thermo_style command, often includes temperature and pressure values. As explained on the doc page for thethermo_style command, the default T and P are setup by the thermo command itself. They are NOT the ones associated with any thermostatting or barostatting fix you have defined or with any compute that calculates a temperature or pressure. Thus if you want to view these values of T and P, you need to specify them explicitly via a thermo_style custom command. Or you can use the thermo_modify command to re-define what temperature or pressure compute is used for default thermodynamic output.” (http://lammps.sandia.gov/doc/Section_howto.html#4_16)

Then I look through the keyword “thermo”, which has only one value “N”, representing the frequency of writing thermodynamics into output. I also note in the peptide example provided by the program, T is defined by “fix”.
Am I right to think that the T and P defined by “fix” will override the default T and P ? If NVE ensemble is used and then no T and P are specified, will the default T and P be used ?

Thanks,

Guozhen

2

Temperatures in LAMMPS (and pressures) are measured by
"computes". See compute temp for example. The thermo
command creates a compute to output the temp. Ditto for
thermostats like fix nvt. Each of those computes has a name
and you can query and output its temperature if you like.
See the thermo_style and fix nvt commands for details. You
can also override which compute is used for thermo output
of T via the thermo_modify command.

Steve