# How do I rectify this error?
**URL:** https://gromacs.bioexcel.eu/t/how-do-i-rectify-this-error/8455
**Category:** User discussions
**Created:** [February 28, 2024, 9:48am UTC](https://gromacs.bioexcel.eu/t/how-do-i-rectify-this-error/8455 "2024-02-28T09:48:16Z")
**Posts on this page:** 2
**Page:** 1
### Author:  [@priyanka](https://gromacs.bioexcel.eu/u/priyanka)
#### Post date: [February 28, 2024, 9:48am UTC](https://gromacs.bioexcel.eu/t/how-do-i-rectify-this-error/8455/1 "2024-02-28T09:48:16Z")
GROMACS version: 2021
GROMACS modification: Yes/No
Here post your question
ERROR 1 [file md\_pull.mdp]:
When the maximum distance from a pull group reference atom to other atoms
in the group is larger than 0.5 times half the box size a centrally
placed atom should be chosen as pbcatom. Pull group 1 is larger than that
and does not have a specific atom selected as reference atom.
ERROR 2 [file md\_pull.mdp]:
When the maximum distance from a pull group reference atom to other atoms
in the group is larger than 0.5 times half the box size a centrally
placed atom should be chosen as pbcatom. Pull group 2 is larger than that
and does not have a specific atom selected as reference atom.
---
### Author:  [@Karis](https://gromacs.bioexcel.eu/u/Karis)
#### Post date: [February 28, 2024, 9:55am UTC](https://gromacs.bioexcel.eu/t/how-do-i-rectify-this-error/8455/2 "2024-02-28T09:55:39Z")
This post should help: [Defining central atom in steered molecular dynamics](https://gromacs.bioexcel.eu/t/defining-central-atom-in-steered-molecular-dynamics/2531)