# Regarding pulling force in smd- distance pulling **URL:** \ **Category:** User discussions\ **Created:** [November 7, 2021, 1:58pm UTC](https://gromacs.bioexcel.eu/t/regarding-pulling-force-in-smd-distance-pulling/3095 "2021-11-07T13:58:03Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![Yogesh](https://avatars.discourse-cdn.com/v4/letter/y/49beb7/32.png) [@Yogesh](https://gromacs.bioexcel.eu/u/Yogesh)\ **Post date:** [November 7, 2021, 1:58pm UTC](https://gromacs.bioexcel.eu/t/regarding-pulling-force-in-smd-distance-pulling/3095/1 "2021-11-07T13:58:04Z")
Hi I tried to pull a ion through protein channel. But force is increasing exponentially with time which is quite unexpected. At some portion of channel force should have lowered. What could be the possible explanation? I used 100 kjoule force and pulling distance is around 5nm . ---
**Author:** ![Yogesh](https://avatars.discourse-cdn.com/v4/letter/y/49beb7/32.png) [@Yogesh](https://gromacs.bioexcel.eu/u/Yogesh)\ **Post date:** [November 9, 2021, 9:44am UTC](https://gromacs.bioexcel.eu/t/regarding-pulling-force-in-smd-distance-pulling/3095/2 "2021-11-09T09:44:33Z")
![Screenshot from 2021-11-09 15-11-46](https://europe1.discourse-cdn.com/flex017/uploads/bioexcel1/original/2X/e/eaf26919a249b757ba7351e7aff762d1ca0c9d10.png) In continuation of previous mail please find attached force plots for NAMD and gromacs. my pull parameters are ; Pull code pull = yes pull\_ncoords = 1 ; only one reaction coordinate pull\_ngroups = 2 ; two groups defining one reaction coordinate pull\_group1\_name = LIG pull\_group2\_name = a\_10042 pull\_coord1\_type = umbrella ; harmonic potential pull\_coord1\_geometry = distance ; simple distance increase pull\_coord1\_dim = N N Y ; pull along z pull\_coord1\_groups = 1 2 ; groups 1 (Chain A) and 2 (Chain B) define the reaction coordinate pull\_coord1\_start = yes ; define initial COM distance \> 0 pull\_coord1\_rate = 0.01 ; 0.01 nm per ps = 10 nm per ns pull\_coord1\_k = 100 ; kJ mol^-1 nm^-2 it will be great if someone can guide me whats the difference in both pullings? why isnt energy lowering in gromacs?