I want to run some MD in LAMMPS, but always had different error. After it runs, the pressure had negative value that is illogical. How can I run the following runs with lammps?
- minimizing the system
- NPT run for 10000 step
- NVT run for 10000 step
The time step is 1 fs and the thermostat and barostat is Berendsen.
that’s too little info to work with. but most likely it’s a bad “computational physics” issue (like, for instance, too high density + too low temperature in a LJ system)
A negative pressure is not “illogical”, and it is just as normal as a positive pressure; it is just a matter of expanding or shrinking, not bad physics/dynamics.
What were the errors exactly? You can run these three steps using minimize and run commands plus appropriate fixes (with proper dampings). Make sure a 1 fs timestep size is appropriate.
A negative pressure is not "illogical", and it is just as normal as a
positive pressure; it is just a matter of expanding or shrinking, not bad
Indeed. Atmospheric pressure at sea level (~1 Bar) is practically
zero, so fluctuations around this value are frequently negative. For
the systems I've looked at, these fluctuations are frequently about
+/- 10^2 Bar or larger.