# Materials with several hydrogen isotopes

**URL:** <https://festim.discourse.group/t/materials-with-several-hydrogen-isotopes/183>\
**Category:** User Support\
**Created:** [August 26, 2026, 2:42pm UTC](https://festim.discourse.group/t/materials-with-several-hydrogen-isotopes/183 "2026-08-26T14:42:29Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![miklavrent](https://yyz2.discourse-cdn.com/free1/user_avatar/festim.discourse.group/miklavrent/32/94_2.png) [@miklavrent](https://festim.discourse.group/u/miklavrent)\
**Post date:** [August 26, 2026, 2:42pm UTC](https://festim.discourse.group/t/materials-with-several-hydrogen-isotopes/183/1 "2026-08-26T14:42:29Z")

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Hi,

I’m doing two isotopes in a multimaterial component. First I need to define materials (W, Cu, CuCrZr); next, volume subdomains with material for each of them. Finally, I define species (D, T). My problem is: before I define species, I can define only one set of parameters (D\_0, E\_D etc) for each material. After species are defined, I have to change from one to two sets of parameters - how to do this?

Alternatively, I attempted to define species first, then it is possible to define materials with separate parameters for each species. But species require subdomains, and subdomains require materials - looks very circular. 😵‍💫

Mikhail

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**Author:** ![remidm](https://yyz2.discourse-cdn.com/free1/user_avatar/festim.discourse.group/remidm/32/4_2.png) [@remidm](https://festim.discourse.group/u/remidm)\
**Post date:** [August 26, 2026, 6:04pm UTC](https://festim.discourse.group/t/materials-with-several-hydrogen-isotopes/183/2 "2026-08-26T18:04:26Z")

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Hi @miklavrent

You can first define species with no subdomains, then define materials, then subdomains and finally,

```python
for spe in my_model.species:
    spe.subdomains = my_model.volume_subdomains 

```

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<div class="post-metadata">

**Author:** ![miklavrent](https://yyz2.discourse-cdn.com/free1/user_avatar/festim.discourse.group/miklavrent/32/94_2.png) [@miklavrent](https://festim.discourse.group/u/miklavrent)\
**Post date:** [August 27, 2026, 2:48pm UTC](https://festim.discourse.group/t/materials-with-several-hydrogen-isotopes/183/3 "2026-08-27T14:48:14Z")

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Thank you Remi,

It works like this!

Mikhail