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Messages - joannewanghf

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I modified atom coordinates of C2H2 and problem solved. But I don't know why.

Dear Prof. Dubbeldam and RASPA community,
I have used RASPA 2.0.37 for gas adsorption simulations in a Cu-MOF in last months.

I built myown forcefiled files based on Dubbeldam2012MIL-101, and got reasonable isotherm data for CH4 and CO2 adsorption. But encountered ENERGY DRIFT warning when I move to C2H2 (acetylene) adsorption, even at low pressure (e.g. 24Pa, 298K).

I found this warning would be eliminated when the charge of C_C2H2 and H_C2H2 equal to zero, but it leads to very low absolute adsorption (i.e., 0.02 cm^3/g. the experimental result is ~52 cm^3/g).  When I set the charge of C_C2H2 and H_C2H2 as 0.278, I got close adsorption as experiment but ENERGY DRIFT warning occurs.

I tried to change, respectively, radii of Cu, C_C2H2 and H_C2H2 in pseudoatom.def, L-J parameters of Cu, C_C2H2 and H_C2H2 in force_field_mixing_rules.def. All of attempts led to dramatically changes in amount of total ENERGY DRIFT and seems no rules. Besides, I performed two runs, respectively, with the same input files, it gives very different total energy drift.

So how can I fix this problem, and how to build a proper forcefield for specific systems, is there some guidelines or skills?

Some parameters used in one of my jobs with the smallest total energy drift (1.11544) is attached :

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