# nonpriodic boundry condition

Dear lammps users,
How can I control the temperature in nonperiodic boundary condition without controlling volume with NVE? I want to calculate density at the ideal gas state, so I need to control temperature, but thermostats have no time integration.
best regards

Can I say that NPT with 0.00 atm pressure is the same as nonperiodic boundary condition?

best

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Can I say that NPT with 0.00 atm pressure is the same as nonperiodic
boundary condition?

​no.

Dear lammps users,
How can I control the temperature in nonperiodic boundary condition
without controlling volume with NVE?

​please note, that there is a significant difference between using fix nve
and an NVE ensemble. you *can* achieve an NVE ensemble by using fix nve,
but using fix nve does not automatically result in an NVE ensemble. this
has been explained on this mailing list many, many times.

besides, fix nve does *NOT* control the volume. ​ in fact, to be compatible
with creating an NVE ensemble is *MUST NOT* do *any* manipulations of the
system, neither volume nor (kinetic) energy.

​​fix nve is fully compatible with non-periodic boundaries.

I want to calculate density at the ideal gas state, so I need to control
temperature, but thermostats have no time integration.

however, you are not making much sense here. using a thermostat for an
ideal gas is pointless, since ideal gas particles do not interact; so how
could they couple with a reservoir?

​also, there is not such thing as an "ideal gas state". an ideal gas is a
well defined thermodynamic entity. there is little value to doing
simulations of an ideal gas, since all its properties can be obtained
analytically.

besides, what has this all to do with periodic-boundary conditions?

axel.

Dear Dr. Axel,
I have this much information from article and there is no more than this almost anywhere.

"To calculate the cohesive energy
density, the average internal energy and molar volume of the
liquid were obtained from the liquid simulation, and the average
internal energy of the ideal gas was obtained by simulating a
single [bmim][PF6] ion pair at the same temperature as the liquid
but at zero pressure (i.e., no periodic boundary conditions)."

could you please help me with this exhausting issue. As you said it makes no sense to control temperature, but I need internal energy(total energy) in this temperature to calculate something else.

Best regards

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Dear lammps users,
How can I control the temperature in nonperiodic boundary condition
without controlling volume with NVE?

​please note, that there is a significant difference between using fix
nve and an NVE ensemble. you *can* achieve an NVE ensemble by using fix
nve, but using fix nve does not automatically result in an NVE ensemble.
this has been explained on this mailing list many, many times.

besides, fix nve does *NOT* control the volume. ​ in fact, to be
compatible with creating an NVE ensemble is *MUST NOT* do *any*
manipulations of the system, neither volume nor (kinetic) energy.
why in my simulation volum is constant?( nonperiodic and fix NVE)

​if nothing changes the volume, it will remain constant.

however, you seem to be missing important conceptual points about what you
are trying to do, and that is really very worrisome. you need tutoring in
statistical thermodynamic beyond what a mailing list can provide.

for example, in a non-periodic system, the volume is effectively infinite
(unless you create artificial boundaries through a wall fix). however, that
is not practical to do with a simulation program using domain decomposition
parallelization. so you can set ​it to any size you want, for as long as
the atoms remain in that volume.
so you can use fixed boundaries with a safety margin ​or you can have the
simulation program update the boundaries in such a way, as the ​box adjust
to the extent of the included atoms (aka shrinkwrap boundaries). in any
case, since you have no interactions with peridodic images the
thermodynamic properties are the same (except pressure, which is not well
defined under these circumstances and compute pressure computes the
pressure for a periodic or bounded system).

axel.