# (no subject)

Hi everybody
I work with windows version of lammps, my work is simulation a box of
200 ionic liquid, I use this script in input file
atom_style full
pair_style lj/cut/coul/long 15.0
fix 1 all nve
I should Comparison the result of this NVE ensemble , with a NPT
ensemble that already simulated , the temperature that resulted from
NVE is about 205 K , but the temperature I import to NPT is 398.15 K ,
all condition for two ensemble is equal and I use the resulted volume
of NPT ensemble for initial volume for NVE , how can I change the
input or data file of NVE ensemble in order that equilibrium
temperature increase to 398.15 K ( the same value with NPT ensemble) ?
Can I change the initial energy? How?
sincerely

Hi everybody
I work with windows version of lammps, my work is simulation a box of
200 ionic liquid, I use this script in input file

200 molecules is not a fairly small system...

atom_style full
pair_style lj/cut/coul/long 15.0
fix 1 all nve

this is not the *entire* script.

I should Comparison the result of this NVE ensemble , with a NPT
ensemble that already simulated , the temperature that resulted from
NVE is about 205 K , but the temperature I import to NPT is 398.15 K ,

what do you mean by this? for such a small system, the instantaneous
temperature will fluctuate quite significantly, so determining the
termperature to two digits after the decimal point is not realistic
unless you do something very unrealistic in your simulation setup.

all condition for two ensemble is equal and I use the resulted volume
of NPT ensemble for initial volume for NVE , how can I change the
input or data file of NVE ensemble in order that equilibrium
temperature increase to 398.15 K ( the same value with NPT ensemble) ?

since you are not adding or removing kinetic energy in your NVE run,
you will first have to equilibrate your system. if the system is not
in equilibrium, the distribution between kinetic and potential energy
will change, and depending on whether your initial potential energy
was too high or too low, the kinetic energy will rise or fall during
the process.

Can I change the initial energy? How?

have you seen the velocity command? or you can run for a while with a
thermostat until your system is equilibrated and then turn it off.

this all sounds like you need to have a good long chat with your
adviser or whoever is training you in doing MD about the topic of
equilibration. understanding this topic is crucial for doing
meaningful MD simulations.

axel.

ok ,
How can I change the initial energy with velocity command in a NVE ensemble?
excuse me but I'm new and this forum has not any rules about level of question ,

ok ,
How can I change the initial energy with velocity command in a NVE ensemble?

Try reading the documentation.

excuse me but I’m new and this forum has not any rules about level of question ,

You have been around long enough to see me explaining the difference between a classroom or a discussion with your adviser and a valid question.

What you have asked has little do with lammps itself, but the understanding of MD in general. You cannot do meaningful simulations without that understanding and learning these fundamentals is something you should have done even before trying to use lammps.

You will see, that if you make an effort and follow this advice, the benefit will be manifold and worth the effort and inconvenience.

You can use the velocity command to rescale the velocities to a new
temperature, which is changing the energy.

Steve