# Simple Pulling script 1D 1 group **URL:** https://gromacs.bioexcel.eu/t/simple-pulling-script-1d-1-group/12100 **Category:** User discussions **Tags:** pull-code **Created:** [May 17, 2025, 10:35am UTC](https://gromacs.bioexcel.eu/t/simple-pulling-script-1d-1-group/12100 "2025-05-17T10:35:06Z") **Posts on this page:** 1 **Page:** 1
### Author: ![lazzari26](https://avatars.discourse-cdn.com/v4/letter/l/9f8e36/32.png) [@lazzari26](https://gromacs.bioexcel.eu/u/lazzari26) #### Post date: [May 17, 2025, 10:35am UTC](https://gromacs.bioexcel.eu/t/simple-pulling-script-1d-1-group/12100/1 "2025-05-17T10:35:06Z")
I always struggled in finding a good algorithm for pulling in GROMACS, the tool is good but the documentation is awful. Here I’m just sharing a good script that work for pulling in 1 dimension (x-axis), with a constant force, just one group (WATER) in relation to the simulation box, with periodic boundary conditions (pbc). ; ---------- constant‑force pulling (one coordinate) ---------- pull = yes pull-ncoords = 1 ; one reaction coordinate pull-ngroups = 1 ; one group is enough – reference is the box pull-group1-name = WATER ; must match the name in index.ndx ; What type of force? pull-coord1-type = constant-force ; linear potential → constant F ; Geometry: along a fixed vector that respects PBC pull-coord1-geometry = direction-periodic pull-coord1-groups = 1 0 ; WATER vs. absolute reference pull-coord1-vec = 1 0 0 ; +x pull-coord1-dim = Y N N ; only x component is active ; Magnitude of the force (kJ mol⁻¹ nm⁻¹) ; k (mdp units) = F(pN) = F(10-12N)/ 1.66054 pull-coord1-k = 300 ; ≈ 500 pN on the COM pull-pbc-ref-prev-step-com = yes pull-group1-pbcatom = 17996 ; reference atom from the WATER group ; this helps with the size of the box problem for PBC pull-coord1-start = yes ; take current COM as zero pull-print-ref-values = yes ; handy for analysis ; --------------------------------------------------------------- Hopes it can help anyone…