Dear all,

I am currently working on GCMC calculation of CO2 adosption in MOFs.

I started with a simple test with CO2 in a empty box and I played with several Coloumbic energy calculation method.

I tried three different setting for charge calculation.

(1)

pair_style lj/cut 12

(2)

pair_style lj/cut/coul/cut 12 12

(3)

pair_style lj/cut/coul/long 12.0

kspace_style ewald 1.0e-4

kspace_modify mesh 500 500 500 order 50

The first method did not include the electrostatic interactions, I expected the gas in the box would be slightly higher than this.21

The second method provide surprisingly high negative coloumbic energy and filled the box with hundreds of gas molecules. It means that the molecules are strongly attracting each other, right ?

The third method give high positive E_coul and high negative E_long, so it ends up with slightly negative value. The number of gas molecules is slightly less than the calculation without coloumbic interactions.

I am confused what is happening with the second and third method and not sure how to deal with that.

I have attached the files needed for the calculations.

I have also tried the three for CO2 in MOF. From my personal experience, the Coloumbic energy contributes to 5%-30% of the total uptake. However, the third method shows a lower numbers of uptake than the one without coloumbic interactions. And the second method shows a ten times higher uptake than the one without coloumbic interactions.

I am confused about the results. Could someone tell me what is the right way to describe coloumbic interactions.

Looking forward to your reply.

Many thanks in advance!

in.lammps (926 Bytes)

test.data (1.19 KB)

CO2.mol (397 Bytes)