# Topology file for metal ion

**URL:** <https://gromacs.bioexcel.eu/t/topology-file-for-metal-ion/8218>\
**Category:** User discussions\
**Created:** [February 4, 2024, 2:50pm UTC](https://gromacs.bioexcel.eu/t/topology-file-for-metal-ion/8218 "2024-02-04T14:50:03Z")\
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**Author:** ![milosz.wieczor](https://avatars.discourse-cdn.com/v4/letter/m/b19c9b/32.png) [@milosz.wieczor](https://gromacs.bioexcel.eu/u/milosz.wieczor)\
**Post date:** [February 4, 2024, 11:08pm UTC](https://gromacs.bioexcel.eu/t/topology-file-for-metal-ion/8218/6 "2024-02-04T23:08:16Z")

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Then, as I said, if the interaction is strong enough, it should be sufficient to have them both in a bound state at the beginning of the simulation, without any additional bonds specified in the topology.

Of course, interactions with ions are never perfectly modeled in additive (non-polarizable) force fields so it’s an open question whether a naive approach will work for you; if it’s somehow experimentally known that the two should stay together and in the simulation they don’t, one can try out different sodium parameter sets, or simply add a restraint. This very much depends on the ultimate purpose of your simulation.

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