[lammps-users] volume increases very much

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1

Dear all,

I am trying to simulate a system that consists of about 52000 atoms, for fixing pressure to 1.013 bar and temperature to 300 K i used NPT ensemble. after some steps pressure and temperature fluctuation about above values. But volume increases very much! then density of mass for this system is unphysical probably. would you help me please.

Thanks
Yasti

2

Dear all,

I am trying to simulate a system that consists of about 52000 atoms, for
fixing pressure to 1.013 bar and temperature to 300 K i used NPT ensemble.
after some steps pressure and temperature fluctuation about above values.
But volume increases very much! then density of mass for this system is
unphysical probably. would you help me please.

it has been discussed on this list several times recently.
please _first_ equilibrate your system with a fixed volume
and only then switch to npt. my recommendation is to do this
with fix nve and fix langevin with parameters set to guarantee
good equipartitioning of your kinetic energy.

cheers,
   axel.

3

The only reason the box volume will increase in NPT is b/c the
system pressure is much higher than the target pressure you
request. NPT responds by increasing the box volume to reduce
the pressure.

Steve