# Hard Spheres Brownian Dynamics LJ Energy **URL:** \ **Category:** User discussions\ **Created:** [September 17, 2020, 3:33pm UTC](https://gromacs.bioexcel.eu/t/hard-spheres-brownian-dynamics-lj-energy/827 "2020-09-17T15:33:39Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![cintia.vequi](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/cintia.vequi/32/374_2.png) [@cintia.vequi](https://gromacs.bioexcel.eu/u/cintia.vequi)\ **Post date:** [September 17, 2020, 3:33pm UTC](https://gromacs.bioexcel.eu/t/hard-spheres-brownian-dynamics-lj-energy/827/1 "2020-09-17T15:33:39Z")
GROMACS version: 2020.3 GROMACS modification: No Dear all, I am trying to perform a BD of 2.5nm and 50 nm radius hard spheres. I created a itp file for them with C12 and C6 for the LJ interactions. However, I am getting the value 0 for the LJ energy in the log file and I do not know why. Since the LJ is the only interaction present in the system, it should not be zero. Right? My itp for the hard spheres is listed below. Thank you so much, Cintia ; Topology of solid particles. [defaults] ; nb-type combination-rule gen-pairs fudgeLJ fudgeQQ 1 1 no [atomtypes] ;type mass charge ptype c6 c12 FA 4.8e+04 0.000 A 0 6.08984e+08 FB 3.0e+08 0.000 A 0 2.49440e+24 [moleculetype] ;name nrexcl F005 1 ; sigma=05nm Epsilon= 0.6236 kJmol-1 mass= 48000 Da C12= 6.08984e+08 kJmol-1nm12 [atoms] ; nr type resnr residu atom cgnr charge mass 1 FA 1 F005 FA 0 0.00 4.8e+04 [moleculetype] ;name nrexcl F100 1 ; sigma=100nm Epsilon= 0.6236 kJmol-1 mass= 3.0e+08 Da C12= 2.49440e+24 kJmol-1nm12 [atoms] ; nr type resnr residu atom cgnr charge mass 1 FB 1 F100 FB 0 0.00 3.0e+08 ---
**Author:** ![jalemkul](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/jalemkul/32/18_2.png) [@jalemkul](https://gromacs.bioexcel.eu/u/jalemkul)\ **Post date:** [September 17, 2020, 4:36pm UTC](https://gromacs.bioexcel.eu/t/hard-spheres-brownian-dynamics-lj-energy/827/2 "2020-09-17T16:36:00Z")
> [@cintia.vequi](#): > > Since the LJ is the only interaction present in the system, it should not be zero. Right? With C6 = 0, the LJ potential is always zero. ---
**Author:** ![cintia.vequi](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/cintia.vequi/32/374_2.png) [@cintia.vequi](https://gromacs.bioexcel.eu/u/cintia.vequi)\ **Post date:** [September 18, 2020, 6:51am UTC](https://gromacs.bioexcel.eu/t/hard-spheres-brownian-dynamics-lj-energy/827/3 "2020-09-18T06:51:59Z")
Thank you so much for your comment. After I read it, I realized why it is zero.