which ensemble should I choose when I use "fix deposit"

Dear all,
     I have a question about which ensemble I should use together with the "fix deposit". I was suggested by using NVE with langewin thermostat, combined with "fix deposit", but now I just think that when we use "fix deposit", the atom in the system is changing from time to time, so what is the reliable reason for me to use the NVE ensemble?
     Any suggestions? Looking for your reply.
Best
XJ

Dear all,
I have a question about which ensemble I should use together with the "fix deposit". I was suggested by using NVE with langewin thermostat, combined with "fix deposit", but now I just think that when we use "fix deposit", the atom in the system is changing from time to time, so what is the reliable reason for me to use the NVE ensemble?
Any suggestions? Looking for your reply.

please note, that fix nve doesn't _enforce_ an nve ensemble or guarantees it.
all it does is to propagate atoms in a way that is consistent with nve, i.e.
don't change the volume of the simulation cell and don't add/remove any
energy. everything else goes on top of that.

HTH,
    axel.

Hi, many thanks for reply.

While I still have more questions:
1. How do I test whether the nve is fit for my deposit simulation?
2. Is it possible to use fix GCMC together with fix nve, because in deposition simulation, Nose−Hoover themostat can not describe the system with a changing atom number.
3. Why in the simulation, it can not evaporate by itself like the real experiments?

Have a nice weekend!

XJ

Hi, many thanks for reply.

While I still have more questions:
1. How do I test whether the nve is fit for my deposit simulation?

what i would do for this is to have a 3 layer setup like this:

11111111111111111111111111
22222222222222222222222222
22222222222222222222222222
22222222222222222222222222
33333333333333333333333333

atoms in 1 and 2 are integrated with fix nve
atoms in 3 are not integrated.
atoms in 2 are also thermalized with fix langevin
using a shorter time constant for equilibration and
a longer time constant for production.

the 3 atoms make sure your slab doesn't
move and appear as being on top of a bulk
solid. the langevin thermostat on atoms in
2 will make it looks as if your slab is thermally
coupled to bulk and for 1 and the deposited
atoms, you don't need to exchange kinetic
energy, since they do so in exactly a realistic
way through coupling to other atoms.

2. Is it possible to use fix GCMC together with fix nve, because in deposition simulation, Nose−Hoover themostat can not describe the system with a changing atom number.

sure.

3. Why in the simulation, it can not evaporate by itself like the real experiments?

what cannot evaporate how and where?

axel.

Many thanks again

3. Why in the simulation, it can not evaporate by itself like the real experiments?

what cannot evaporate how and where?

Because in the vapor deposit growth, there is still some evaporate from the substrate, but recently from the MD results it seem no evaporate by using fix nve & fix deposit
While in my previous results, which I put all the deposit atoms in the upper part in initial configuration and let these atoms to deposit on the substrate, i.e. the total atoms in system will not change and I can use fix nvt, in this system I can observe some evaporating atoms from substrate.

I do not know why. And by using fix deposit, I think is much better than my previous methods, but I also want to some evaporating atoms, which will like the real experiments.

Any comments?

Best
XJ

Many thanks again

3. Why in the simulation, it can not evaporate by itself like the real experiments?

what cannot evaporate how and where?

Because in the vapor deposit growth, there is still some evaporate from the substrate, but recently from the MD results it seem no evaporate by using fix nve & fix deposit
While in my previous results, which I put all the deposit atoms in the upper part in initial configuration and let these atoms to deposit on the substrate, i.e. the total atoms in system will not change and I can use fix nvt, in this system I can observe some evaporating atoms from substrate.

I do not know why. And by using fix deposit, I think is much better than my previous methods, but I also want to some evaporating atoms, which will like the real experiments.

Any comments?

whether you evaporate atoms depends on the velocity with which
you hurl atoms at the surface. if your increase it, you'll see atoms
been kicked out of the surface. the longer you do that, the more
it'll also be heating up the impact area and then it will be easier
to evaporate atoms. since MD simulations typically cover only
a very short time span, you don't see as many event as you
may expect.

cheers,
    axel.