Grimme D3 Correction to CO2 System @ 1200 K

[Michela Benazzi]

Hello everyone,

I have posted here before about my simulations involving liquid metal + CO2. I realized that my extremely high T, P were arising once I added CO2 instead of vacuum on top of a previously converged 2D periodic slab of liquid metal.

I am now trying to run DFT on CO2 alone at 1200 K. I attached the files I used before and after adding the Grimme D3 correction: I thought it would "fix it" by accounting for long-range vdW forces that I was not accounting for before, but nothing has changed. Is there anything else I am missing?

I have gotten comments before on how my initial CO2 system is too ordered (I generate it with Python): I am just curious about how others prepare an initial gas structure before using DFT to get optimized geometry. Should I run GEO_OPT first?

Is that even the main problem with my work?

Thank you so much! Best,

Michela

[Quentin Pessemesse]

Hello,

About building initial configurations, packmol is a great free option to generate "disordered" inital structures. It's very easy to use.

Regarding your CO2 cell, you have 36 CO2 molecules in a cell with a volume of around ~ 2,0 × 10^-27 m³. This is an ideal gas pressure of around 3000 bars, so you are indeed looking at a very dense phase of CO2 and not CO2 gas (of course this is no longer an ideal gas and the 3000 bar figure is not really meaningful, but your initial density is ~1300 kg/ m^-3 , which is between the densities of liquid and solid CO2). Are you sure this is what you mean to look at?

I hope someone can chime in regarding the barostat as it's not something I am very familiar with.

Take care :)

Quentin

[Michela Benazzi]

Hi Quentin, thank you so much for the recommendation - I will look into packmol!!

Yes, the idea would be to introduce a highly pressurized flow of CO2 into our system - to be honest, my advisor and I have not really worked out how pressurized it should be, so I will look into it.

Michela

[Quentin Pessemesse]

I’m glad I could help! I have no idea what your system is, but keep in mind that gases are very dilute and even tens of bars of CO2 might only amount to a few molecules in the vacuum above your surface. For instance at the critical point, 73 bars/31 °C, the density is a bit more than 13 molecules of CO2 in the volume of your simulation. It will often be much less at high temperature.

Good luck 🔥

Le 14 févr. 2025 à 14:15, Michela Benazzi <bnzmi...@gmail.com> a écrit :

Hi Quentin, thank you so much for the recommendation - I will look into packmol!!

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[Ari Paavo Seitsonen]

Hello Michela, CC: Forum

  Please have a look on the https://manual.cp2k.org/cp2k-2024_1-branch/CP2K_INPUT/FORCE_EVAL/DFT/XC/VDW_POTENTIAL/PAIR_POTENTIAL.html instead (the section on &PAIR_POTENTIAL goes into the section &XC, not &ATOM).

  Another issue, you exclude the periodicity in the third direction (&POISSON / PERIODIC XY); is that a valid assumption, that the molecules would not desorb from the "slab" at such high a temperature?

    Greetings from Paris,

       apsi

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