# Query regarding non-bonded parameter combination **URL:** \ **Category:** User discussions\ **Created:** [June 5, 2020, 3:09pm UTC](https://gromacs.bioexcel.eu/t/query-regarding-non-bonded-parameter-combination/249 "2020-06-05T15:09:51Z")\ **Posts on this page:** 1\ **Page:** 1
**Author:** ![snehasis.chatterjee](https://avatars.discourse-cdn.com/v4/letter/s/90db22/32.png) [@snehasis.chatterjee](https://gromacs.bioexcel.eu/u/snehasis.chatterjee)\ **Post date:** [June 5, 2020, 3:09pm UTC](https://gromacs.bioexcel.eu/t/query-regarding-non-bonded-parameter-combination/249/1 "2020-06-05T15:09:51Z")
Dear Gromacs users, I am trying to perform a simulation for a protein-DNA system using GROMACS 2019. I would like to use both CHARMM22 and AMBER99SB-ILDN force fields for force field comparison. non-bonded settings for AMBER99SB-ILDN: coulombtype = pme rcoulomb = 1.0 vdwtype = Cut-off rvdw = 1.0 pme\_order = 4 fourierspacing = 0.16 non-bonded settings for CHARMM22: coulombtype = pme rcoulomb = 1.2 vdwtype = Cut-off vdw-modifier = Force-switch rvdw\_switch = 1.0 rvdw = 1.2 pme\_order = 4 fourierspacing = 0.16 During production run tpr file generation (using grompp), I saw the following messages: **using CHARMM22 force field:** **Generated 97877 of the 97903 non-bonded parameter combinations** **Generating 1-4 interactions: fudge = 1** **Generated 64492 of the 97903 1-4 parameter combinations** **using AMBER99SB-ILDN force field:** **Generated 2211 of the 2211 non-bonded parameter combinations** **Generating 1-4 interactions: fudge = 0.5** **Generated 2211 of the 2211 1-4 parameter combinations** Significantly very few non-bonded parameter combinations were generated during grompp, using AMBER99SB-ILDN force field compared to CHARMM22. I am confused regarding this issue. Any kind of advice/ suggestions will be deeply appreciated. Thanks in advance, Snehasis Chatterjee