Why lammps cannot control pressure and temperature to what I have fixed????

Thanks for your answering.

yeah…you are right.
And I wonder what Tdamp and Pdamp mean in fix npt cammand. When I run 400,000 steps,the temp nearly arrives at the target temp, but the pressure far not. Why the press fix is too much slower than temp? The damp values seem to have a influence on the number of teps needed to reach the temp.& press. which I have fixed.
How can i choose the value of Tdamp and Pdamp so that it can effectly reduce the steps needed to reach the point I set???

Thanks.

If I had ten hours to cut woods,I will spend eight sharping my axe and two for cutting.

11年4月4日,周一, Axel Kohlmeyer [email protected] 写道:

Thanks for your answering.

yeah...you are right.
And I wonder what Tdamp and Pdamp mean in fix npt cammand. When I run 400,000 steps,the temp nearly arrives at the target temp, but the pressure far not. Why the press fix is too much slower than temp? The damp values

in condensed system pressure fluctuates a lot. you have to use a large damping
time, or else the algorithm will become unstable. during equilibration, you can
"play" with the 'drag' option. that will not give you a correct ensemble, but
keeps the algorithm from freaking out, when you overload it.

seem to have a influence on the number of teps needed to reach the temp.& press. which I have fixed.
How can i choose the value of Tdamp and Pdamp so that it can effectly reduce the steps needed to reach the point I set???

it is not that easy to predict when your system is
properly equilibrated and how to get there.
it particularly depends on how far away from equilibrium you are starting.
also, different thermostat algorithms have different characteristics.
you want to start with stronger thermostatting (shorter damping time)
and then increase the damping time when you are close enough to
equilibrium. it is advisable to monitor the simulation and experiment
a bit, until a reasonable setup is found.

axel.