Mixture CO2-N2

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1

Hi,

I’m trying to simulate a mixture of CO2 and N2 and I want to fix a pressure of 1 atm. Could you suggest me the best way to do this? I usually calculate the number of molecules necessary to obtain the pressure that I want through NIST database, but I can’t do this with a mixture.

Once this is done, how can I compare the results obtained with literature values? Do you have databases to recommend for binary mixture? Because I didn’t find anything in literature similar to my operative conditions.

Thanks

Simona

2

If you have a mixture with a specific molar ratio, for instance 1-to-1, then you can run an MD simulation in the NPT ensemble with a barostat maintaining the pressure at 1 atm (see fix npt in the documentation). For the case of the mixture you can assume ideal mixing as a good starting point for what your initial box volume should be and the barostat will adjust it accordingly to maintain a pressure of 1 atm.

You should also do a box size analysis to see how many molecules of CO2 and N2 you need to make sure that properties are not changing and averages are good. i.e. 1 molecule of CO2 and 1 molecule of N2 is not enough so you should figure out how much is enough. Once this is done you can try to compare to literature values. I am not aware of any such database that you are mentioning, but the system that you are studying is an incredibly common one (especially at atmospheric conditions) so the amount of literature should be vast. Dig harder! I suggest browsing the journal of membrane science if you haven’t already.

Good luck,
Best,
Dylan

3

Thank you very much,

your suggestion is very useful. A doubt came to me. What do you mean by “do a box size analysis to see how many molecules of CO2 and N2 you need to make sure that properties are not changing and averages are good”? Can the number of molecules be calculated in any way, or should I make attempts? If I can calculate it, can you suggest the right way?

Thanks,

Simona

4

For most gases at ambient condition using the ideal gas equation give a reasonable estimate.

axel.