# Open .FChk file

**URL:** <https://discuss.avogadro.cc/t/open-fchk-file/3860>\
**Category:** Suggestions\
**Created:** [June 6, 2022, 6:37pm UTC](https://discuss.avogadro.cc/t/open-fchk-file/3860 "2022-06-06T18:37:50Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![Renyun\_Zhang](https://discuss.avogadro.cc/user_avatar/discuss.avogadro.cc/renyun_zhang/32/1010_2.png) [@Renyun\_Zhang](https://discuss.avogadro.cc/u/Renyun_Zhang)\
**Post date:** [June 6, 2022, 6:37pm UTC](https://discuss.avogadro.cc/t/open-fchk-file/3860/1 "2022-06-06T18:37:50Z")

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It seems the version 1.96 is sensitive to the upper and lowercase of letters in the file format. For example: if the file format is “.FChk”, Avogadro will report an error. However, if one changes it to “.fchk”, it works pretty fine.  
In the older version, when open a FChk file, the molecular orbitals will be listed at the right side of the window, but it is not shown in the version 1.96. I would suggest to have it back.  
The color of the surface (molecular orbitals and electron density) could not be customised.

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**Author:** ![ghutchis](https://discuss.avogadro.cc/user_avatar/discuss.avogadro.cc/ghutchis/32/456_2.png) [@ghutchis](https://discuss.avogadro.cc/u/ghutchis)\
**Post date:** [June 7, 2022, 3:35pm UTC](https://discuss.avogadro.cc/t/open-fchk-file/3860/2 "2022-06-07T15:35:15Z")

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> [@Renyun\_Zhang](#):
>
> It seems the version 1.96 is sensitive to the upper and lowercase of letters in the file format. For example: if the file format is “.FChk”, Avogadro will report an error. However, if one changes it to “.fchk”, it works pretty fine.

Hmm. I’ll take a look. What OS are you using?

> [@Renyun\_Zhang](#):
>
> In the older version, when open a FChk file, the molecular orbitals will be listed at the right side of the window, but it is not shown in the version 1.96. I would suggest to have it back.

It’s on the list, but without more coders, it does take time. 🙂

> [@Renyun\_Zhang](#):
>
> The color of the surface (molecular orbitals and electron density) could not be customised.

Yes, it can. I specifically added this to 1.96. Here’s the LUMO of benzene:

 ![Screen Shot 2022-06-07 at 11.33.21 AM](https://discuss.avogadro.cc/uploads/default/original/2X/1/15c48d92f7ee5f24bf221dff4daab98e75f061ed.jpeg)

Click on the “Meshes” line to bring up the configuration options. You can pick the colors and opacity.

 ![Screen Shot 2022-06-07 at 11.34.51 AM](https://discuss.avogadro.cc/uploads/default/original/2X/8/88b7e85c65fe9ff05b4d6df533e8c84fffed5927.jpeg)

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<div class="post-metadata">

**Author:** ![Renyun\_Zhang](https://discuss.avogadro.cc/user_avatar/discuss.avogadro.cc/renyun_zhang/32/1010_2.png) [@Renyun\_Zhang](https://discuss.avogadro.cc/u/Renyun_Zhang)\
**Post date:** [June 7, 2022, 6:08pm UTC](https://discuss.avogadro.cc/t/open-fchk-file/3860/3 "2022-06-07T18:08:14Z")

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I am using MacOS monterey version 12.4.  
The error that showed when I tried to open “.FChk” is: Unable to find a suitable file reader for the selected file.

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<div class="post-metadata">

**Author:** ![ghutchis](https://discuss.avogadro.cc/user_avatar/discuss.avogadro.cc/ghutchis/32/456_2.png) [@ghutchis](https://discuss.avogadro.cc/u/ghutchis)\
**Post date:** [June 9, 2022, 12:03am UTC](https://discuss.avogadro.cc/t/open-fchk-file/3860/4 "2022-06-09T00:03:01Z")

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Thanks for the heads-up… this should fix the problem - at least on my Mac:  
[macOS.dmg](https://github.com/OpenChemistry/avogadrolibs/suites/6852583956/artifacts/264623558)

Hopefully you were able to change the colors?