Why temperature does not maintain in molecular dynamics simulations under NVE ensemble? Dear researchers

Dear researchers

I have a fundamental question about essence of NVE ensemble.
In that, we assume a constant number of particles are kept in fixed volume and their total energy is constant. This looks like having an isolated macroscopic system, like tea in an ideal flask, where no heat or work exchanges would occur.
However, unlike the macroscopic counterpart, one would expect temperature variation (drift) in the case of microscopic (atomic) system. In that case the total energy includes kinetic (KE) and potential (PE) components and temperature would continuously change as a result of KE exchange for PE.

So, I think that is a contradiction?
Why does atomic system under NVE not resemble the isolated, macroscopic system?

Could anybody please give me an illustrating explanation?

Many thanks in advance

Dear researchers

I have a fundamental question about essence of NVE ensemble.
In that, we assume a constant number of particles are kept in fixed volume and their total energy is constant. This looks like having an isolated macroscopic system, like tea in an ideal flask, where no heat or work exchanges would occur.

​no exchange with the environment

However, unlike the macroscopic counterpart, one would expect temperature variation (drift) in the case of microscopic (atomic) system. In that case the total energy includes kinetic (KE) and potential (PE) components and temperature would continuously change as a result of KE exchange for PE.

​in a proper NVE ensemble simulation (i.e. properly equilibrated and with proper choice of settings) the total energy is conserved and fluctuations of KE and PE depend on the system size.

So, I think that is a contradiction?

​no. i don’t see any.​

Why does atomic system under NVE not resemble the isolated, macroscopic system?

​it does.​

Could anybody please give me an illustrating explanation?

please ​pick up a statistical mechanics text book for further explanations.

​axel.​