Help with GCMC Simulation for Water Adsorption in MOF

[had-sham]

Hi Dear RASPA Community,

I am a beginner in using RASPA and currently working on GCMC simulations for water adsorption in a MOF. I'm trying to reproduce data from the literature, where the reported water uptake at maximum relative humidity (i.e., adsorption from air) is around 30 g/g. However, in my simulation, the uptake is significantly lower—close to zero.

I have reviewed my input files multiple times but haven't been able to identify the issue. I would greatly appreciate it if someone could take a look at my simulation setup and provide guidance.
My input files are attached. For reference, the attached files are described below:

File "perfect_charge.def": The CIF file of the MOF structure. Partial charges were obtained using charge equilibration in RASPA.

File "Tip4p": The water molecule definition file.

Thank you very much for your support!

Best regards,

[had-sham]

Hello everyone,

I reviewed the RASPA simulation output and noticed that in the input block, the density and compressibility of water are reported as 848.3 kg/m³ and 0.0000257130, which are values for the liquid phase. Since we're simulating the adsorption of water vapor, how can I resolve this issue?

Thanks!

[Elnaz Jangodaz]

Hi, I'm experiencing the same issue with water uptake — the calculated uptake is zero at partial pressures corresponding to certain relative humidity values. I noticed something unusual: when I set the external pressure to 101325 Pa at 298 K, the simulation gives an uptake value which is similar to paper results at the saturation point. I put a range of 0-101325 pa for external pressure, the resulting isotherm shows the same uptake trend and point, but now with p₀ = 101325 Pa instead of 31.7 kPa, which is the correct saturation pressure. I'm not sure why the uptake appears at such a high pressure, especially since water should already be in liquid form at 101325 Pa. Let me know if you've figured out what the issue might be.