[lammps-users] cannot control Temperature and Pressure together

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1

Hi all,

i am having difficulties in in controlling Temperature and pressure at the same time. The scenarios that i have used are the following.

fix 1 particles npt temp 300.0 300.0 100.0 iso 1.0 1.0 1000.0 dilate partial

Failure concerning the temperature where it becomes very very small.

after i use

fix 1 particles nvt temp 300.0 300.0 100.0

failure even for temperature by itself.

another effort was:

fix 1 particles nvt temp 300.0 300.0 100.0

with a barostat but nothing again.

and finally nve with temp/rescale or thermostat/berendsen and a barostat/berendsen but this effort it produces error from the beginning about the binsize.

In several previous papers that have made something similar with me they only use nve with thermostat. But this is not “physical” correct because there is no control in pressure.
Any suggestions?

Regards
Jim

2

Hi,

i am having difficulties in in controlling Temperature and pressure at the
same time. The scenarios that i have used are the following.
fix 1 particles npt temp 300.0 300.0 100.0 iso 1.0 1.0 1000.0 dilate partial
Failure concerning the temperature where it becomes very very small.

If you are only thermostating only a part of the system (group
particles), you have to:

* compute the temperature of the group you are thermostating
* use fix_modify to assign this temperature to your thermostat

This is detailed in the manual:

Best,
Laurent

3

One clarification on this point. Both fix nvt and fix npt will
create their own compute to calcaulate a termperature they
need. For fix nvt, the new compute will be for the same
group as fix nvt. For fix npt, it will be the "all" group, since
pressure is always computed on group all. So if that
is satisfactory, you don't need to do what Laurent suggests
with fix_modify. The fix nvt/npt doc pages discuss this.

However, if you want to print out those temperature to
monitor what the thermostatting is operating on, you do
need to adjust your thermo output to specifically list
those compute, either via thermo_style custom or thermo_modify temp.
Again see the doc pages for details.

Also, you should not allow a Nose/Hoover thermostat to
operate on tiny temperatures - that will cause problems.
If your system is reasonably well equilibrated, that should
not happen naturally.

Steve