It seems Avogadro was phased out in Ubuntu 20.04 (Focal Fossa) and derivatives like Mint 20 (Ulyana). Now the version available in the repositories is Avogadro 2. If you had Avogadro installed in 18.04, and did a upgrade, it is replaced with Avogadro 2.
The original Avogadro had a very useful feature, where we could generate input files for several Quantum Chemistry packages. Now the problem is, Avogadro 2 doesn't seem to have the input generators as part of the base install, working out-of-the-box. It seems this functionality was moved to a set of plugins. I tried to get them working, by two different routes, but had no sucess so far. I'm describing what I tried to do, if somebody knows how to sort this problem.
First try: Built-in plugin downloader.
Opening Extensions > Plugin Downloader, we are presented the following screen:
By the description, avogenerators is what I'm looking for. When I select it, and click on Download Selected, it tells me the download was sucessful:
But when I go back to the work area, the menus are unchanged, even after reset. So I think this route failed.
Second try: Download with GIT
I seeked some guidance on this issue in the plugin page on github, but found only this remark:
Installing
These scripts need to be installed in a location where the Avogadro 2 application can find them. They use the JSON API described in the Avogadro 2 API documentation, but the best way to learn is to look at the existing scripts and adapt them to your needs.
Anyway, I proceeded to install GIT:
user@machine:~/src$ sudo apt install git-all
And try to clone the plugin repository:
user@machine:~/src$ git clone https://github.com/OpenChemistry/avogenerators.git
Cloning into 'avogenerators'...
remote: Enumerating objects: 211, done.
remote: Total 211 (delta 0), reused 0 (delta 0), pack-reused 211
Receiving objects: 100% (211/211), 70.05 KiB | 481.00 KiB/s, done.
Resolving deltas: 100% (130/130), done.
From this point it was not clear what to do. I tried to navigate from the Open button into the cloned project folder, and it recognizes the plugin.json file as something that can be opened:
But when you try to load the plugin, it just throws a error:
Third try (Update September 10, 2020): Git download in proper location.
Following the advice in answer comments, I tried to repeat the Git download of the plugins, but this time under ~/.local/share/OpenChemistry/Avogadro/inputGenerators, creating missing subfolders to complete the path, when needed:
user@machine:~$ cd ~/.local/share/OpenChemistry/Avogadro/
user@machine:~/.local/share/OpenChemistry/Avogadro$ ls
other
user@machine:~/.local/share/OpenChemistry/Avogadro$ mkdir inputGenerators
user@machine:~/.local/share/OpenChemistry/Avogadro$ cd inputGenerators/
user@machine:~/.local/share/OpenChemistry/Avogadro/inputGenerators$ git clone https://github.com/OpenChemistry/avogenerators.git
Cloning into 'avogenerators'...
remote: Enumerating objects: 211, done.
remote: Total 211 (delta 0), reused 0 (delta 0), pack-reused 211
Receiving objects: 100% (211/211), 70.05 KiB | 268.00 KiB/s, done.
Resolving deltas: 100% (130/130), done.
user@machine:~/.local/share/OpenChemistry/Avogadro/inputGenerators$ ls
avogenerators
user@machine:~/.local/share/OpenChemistry/Avogadro/inputGenerators$ cd avogenerators/
user@machine:~/.local/share/OpenChemistry/Avogadro/inputGenerators/avogenerators$ ls
dalton.py inputgeneratortest.py nwchem.py pyscf.py
gamessuk.py LICENSE orca.py qchem.py
gaussian.py molpro.py plugin.json README.md
generators.cmake mopac.py psi4.py terachem.py
Still didn't suceed.
Closing remarks
If I didn't just fumbled somewhere, and other people are able to reproduce the problem, I think this is a breaking issue, as the input generators should be critical to many people besides me. It would be nice if the original Avogadro were available in the repositories as a fallback in situations like this. All the tests in this posts were done in a machine running Mint 20 (Ulyana).
Edit
Given Geoff's answer telling the problem is probably related to the locations the plugins are expected to be, I did a search for the Avogadro related locations in my machine, as I think it may be useful.
user@machine:~$ sudo find / -iwholename *avogadro*
/home/user/.local/share/OpenChemistry/Avogadro
/home/user/.local/share/OpenChemistry/Avogadro/other
/home/user/.local/share/OpenChemistry/Avogadro/other/OpenChemistry-avogenerators-8444312
/home/user/.local/share/OpenChemistry/Avogadro/other/OpenChemistry-avogenerators-8444312/gaussian.py
/home/user/.local/share/OpenChemistry/Avogadro/other/OpenChemistry-avogenerators-8444312/LICENSE
/home/user/.local/share/OpenChemistry/Avogadro/other/OpenChemistry-avogenerators-8444312/gamessuk.py
/home/user/.local/share/OpenChemistry/Avogadro/other/OpenChemistry-avogenerators-8444312/inputgeneratortest.py
/home/user/.local/share/OpenChemistry/Avogadro/other/OpenChemistry-avogenerators-8444312/orca.py
/home/user/.local/share/OpenChemistry/Avogadro/other/OpenChemistry-avogenerators-8444312/psi4.py
/home/user/.local/share/OpenChemistry/Avogadro/other/OpenChemistry-avogenerators-8444312/generators.cmake
/home/user/.local/share/OpenChemistry/Avogadro/other/OpenChemistry-avogenerators-8444312/plugin.json
/home/user/.local/share/OpenChemistry/Avogadro/other/OpenChemistry-avogenerators-8444312/terachem.py
/home/user/.local/share/OpenChemistry/Avogadro/other/OpenChemistry-avogenerators-8444312/mopac.py
/home/user/.local/share/OpenChemistry/Avogadro/other/OpenChemistry-avogenerators-8444312/molpro.py
/home/user/.local/share/OpenChemistry/Avogadro/other/OpenChemistry-avogenerators-8444312/pyscf.py
/home/user/.local/share/OpenChemistry/Avogadro/other/OpenChemistry-avogenerators-8444312/nwchem.py
/home/user/.local/share/OpenChemistry/Avogadro/other/OpenChemistry-avogenerators-8444312/.github
/home/user/.local/share/OpenChemistry/Avogadro/other/OpenChemistry-avogenerators-8444312/.github/config.yml
/home/user/.local/share/OpenChemistry/Avogadro/other/OpenChemistry-avogenerators-8444312/.github/PULL_REQUEST_TEMPLATE
/home/user/.local/share/OpenChemistry/Avogadro/other/OpenChemistry-avogenerators-8444312/README.md
/home/user/.local/share/OpenChemistry/Avogadro/other/OpenChemistry-avogenerators-8444312/qchem.py
/home/user/.local/share/OpenChemistry/Avogadro/other/OpenChemistry-avogenerators-8444312/dalton.py
/home/user/.config/OpenChemistry/Avogadro.conf
/usr/lib/python3/dist-packages/avogadro
/usr/lib/python3/dist-packages/avogadro/__pycache__
/usr/lib/python3/dist-packages/avogadro/__pycache__/__init__.cpython-38.pyc
/usr/lib/python3/dist-packages/avogadro/__init__.py
/usr/lib/python3/dist-packages/avogadro/io.cpython-38-x86_64-linux-gnu.so
/usr/lib/python3/dist-packages/avogadro/core.cpython-38-x86_64-linux-gnu.so
/usr/lib/x86_64-linux-gnu/libAvogadroCore.so.1.93.0
/usr/lib/x86_64-linux-gnu/avogadro2
/usr/lib/x86_64-linux-gnu/avogadro2/staticplugins
/usr/lib/x86_64-linux-gnu/avogadro2/staticplugins/VanDerWaals.a
/usr/lib/x86_64-linux-gnu/avogadro2/staticplugins/POVRay.a
/usr/lib/x86_64-linux-gnu/avogadro2/staticplugins/CoordinateEditor.a
/usr/lib/x86_64-linux-gnu/avogadro2/staticplugins/Hydrogens.a
/usr/lib/x86_64-linux-gnu/avogadro2/staticplugins/Spectra.a
/usr/lib/x86_64-linux-gnu/avogadro2/staticplugins/BallStick.a
/usr/lib/x86_64-linux-gnu/avogadro2/staticplugins/commands.a
/usr/lib/x86_64-linux-gnu/avogadro2/staticplugins/Selection.a
/usr/lib/x86_64-linux-gnu/avogadro2/staticplugins/NetworkDatabases.a
/usr/lib/x86_64-linux-gnu/avogadro2/staticplugins/Bonding.a
/usr/lib/x86_64-linux-gnu/avogadro2/staticplugins/Surfaces.a
/usr/lib/x86_64-linux-gnu/avogadro2/staticplugins/ThreeDMol.a
/usr/lib/x86_64-linux-gnu/avogadro2/staticplugins/MolecularProperties.a
/usr/lib/x86_64-linux-gnu/avogadro2/staticplugins/Manipulator.a
/usr/lib/x86_64-linux-gnu/avogadro2/staticplugins/Crystal.a
/usr/lib/x86_64-linux-gnu/avogadro2/staticplugins/CrystalScene.a
/usr/lib/x86_64-linux-gnu/avogadro2/staticplugins/LammpsInput.a
/usr/lib/x86_64-linux-gnu/avogadro2/staticplugins/LineFormatInput.a
/usr/lib/x86_64-linux-gnu/avogadro2/staticplugins/Editor.a
/usr/lib/x86_64-linux-gnu/avogadro2/staticplugins/SpaceGroup.a
/usr/lib/x86_64-linux-gnu/avogadro2/staticplugins/Wireframe.a
/usr/lib/x86_64-linux-gnu/avogadro2/staticplugins/OverlayAxes.a
/usr/lib/x86_64-linux-gnu/avogadro2/staticplugins/VanDerWaalsAO.a
/usr/lib/x86_64-linux-gnu/avogadro2/staticplugins/Meshes.a
/usr/lib/x86_64-linux-gnu/avogadro2/staticplugins/BondCentric.a
/usr/lib/x86_64-linux-gnu/avogadro2/staticplugins/OpenBabel.a
/usr/lib/x86_64-linux-gnu/avogadro2/staticplugins/CopyPaste.a
/usr/lib/x86_64-linux-gnu/avogadro2/staticplugins/CustomElements.a
/usr/lib/x86_64-linux-gnu/avogadro2/staticplugins/Force.a
/usr/lib/x86_64-linux-gnu/avogadro2/staticplugins/MongoChem.a
/usr/lib/x86_64-linux-gnu/avogadro2/staticplugins/MeasureTool.a
/usr/lib/x86_64-linux-gnu/avogadro2/staticplugins/Licorice.a
/usr/lib/x86_64-linux-gnu/avogadro2/staticplugins/PlayerTool.a
/usr/lib/x86_64-linux-gnu/avogadro2/staticplugins/ImportPQR.a
/usr/lib/x86_64-linux-gnu/avogadro2/staticplugins/PluginDownloader.a
/usr/lib/x86_64-linux-gnu/avogadro2/staticplugins/VRML.a
/usr/lib/x86_64-linux-gnu/avogadro2/staticplugins/Navigator.a
/usr/lib/x86_64-linux-gnu/avogadro2/staticplugins/Select.a
/usr/lib/x86_64-linux-gnu/avogadro2/scripts
/usr/lib/x86_64-linux-gnu/avogadro2/scripts/commands
/usr/lib/x86_64-linux-gnu/avogadro2/scripts/commands/scale.py
/usr/lib/x86_64-linux-gnu/libAvogadroQtPlugins.so.1
/usr/lib/x86_64-linux-gnu/libAvogadroQtGui.so.1
/usr/lib/x86_64-linux-gnu/libAvogadroQtPlugins.so.1.93.0
/usr/lib/x86_64-linux-gnu/libAvogadroRendering.so.1.93.0
/usr/lib/x86_64-linux-gnu/libAvogadroIO.so.1
/usr/lib/x86_64-linux-gnu/libAvogadroCore.so.1
/usr/lib/x86_64-linux-gnu/libAvogadroQtOpenGL.so.1.93.0
/usr/lib/x86_64-linux-gnu/libAvogadroQtOpenGL.so.1
/usr/lib/x86_64-linux-gnu/libAvogadroRendering.so.1
/usr/lib/x86_64-linux-gnu/libAvogadroIO.so.1.93.0
/usr/lib/x86_64-linux-gnu/libAvogadroQtGui.so.1.93.0
/usr/lib/x86_64-linux-gnu/libAvogadroQuantumIO.so.1.93.0
/usr/lib/x86_64-linux-gnu/libAvogadroQuantumIO.so.1
/usr/share/doc/avogadro
/usr/share/doc/avogadro/html
/usr/share/doc/avogadro/html/nav_h.png
/usr/share/doc/avogadro/html/index.html
/usr/share/doc/avogadro/html/sync_off.png
/usr/share/doc/avogadro/html/annotated.html
/usr/share/doc/avogadro/html/doxygen.css
/usr/share/doc/avogadro/html/class_avogadro_1_1_about_dialog.html
/usr/share/doc/avogadro/html/bdwn.png
/usr/share/doc/avogadro/html/class_avogadro_1_1_about_dialog-members.html
/usr/share/doc/avogadro/html/namespaces.html
/usr/share/doc/avogadro/html/sync_on.png
/usr/share/doc/avogadro/html/doc.png
/usr/share/doc/avogadro/html/class_avogadro_1_1_about_dialog.png
/usr/share/doc/avogadro/html/class_avogadro_1_1_application-members.html
/usr/share/doc/avogadro/html/class_avogadro_1_1_application.png
/usr/share/doc/avogadro/html/nav_g.png
/usr/share/doc/avogadro/html/class_avogadro_1_1_view_factory.png
/usr/share/doc/avogadro/html/class_avogadro_1_1_main_window.html
/usr/share/doc/avogadro/html/folderopen.png
/usr/share/doc/avogadro/html/open.png
/usr/share/doc/avogadro/html/class_avogadro_1_1_background_file_format-members.html
/usr/share/doc/avogadro/html/closed.png
/usr/share/doc/avogadro/html/dynsections.js
/usr/share/doc/avogadro/html/classes.html
/usr/share/doc/avogadro/html/class_avogadro_1_1_view_factory.html
/usr/share/doc/avogadro/html/nav_f.png
/usr/share/doc/avogadro/html/menudata.js
/usr/share/doc/avogadro/html/class_avogadro_1_1_application.html
/usr/share/doc/avogadro/html/class_avogadro_1_1_background_file_format.html
/usr/share/doc/avogadro/html/bc_s.png
/usr/share/doc/avogadro/html/splitbar.png
/usr/share/doc/avogadro/html/class_avogadro_1_1_rpc_listener.html
/usr/share/doc/avogadro/html/class_avogadro_1_1_menu_builder.html
/usr/share/doc/avogadro/html/tab_h.png
/usr/share/doc/avogadro/html/functions_func.html
/usr/share/doc/avogadro/html/class_avogadro_1_1_background_file_format.png
/usr/share/doc/avogadro/html/jquery.js
/usr/share/doc/avogadro/html/class_avogadro_1_1_view_factory-members.html
/usr/share/doc/avogadro/html/class_avogadro_1_1_rpc_listener.png
/usr/share/doc/avogadro/html/tab_a.png
/usr/share/doc/avogadro/html/doxygen.png
/usr/share/doc/avogadro/html/search
/usr/share/doc/avogadro/html/search/all_2.js
/usr/share/doc/avogadro/html/search/functions_2.html
/usr/share/doc/avogadro/html/search/all_9.html
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/usr/share/doc/avogadro/html/search/functions_0.html
/usr/share/doc/avogadro/html/search/all_8.js
/usr/share/doc/avogadro/html/search/nomatches.html
/usr/share/doc/avogadro/html/search/functions_9.html
/usr/share/doc/avogadro/html/search/all_b.js
/usr/share/doc/avogadro/html/search/functions_5.html
/usr/share/doc/avogadro/html/search/searchdata.js
/usr/share/doc/avogadro/html/search/classes_3.js
/usr/share/doc/avogadro/html/search/functions_c.js
/usr/share/doc/avogadro/html/search/functions_d.js
/usr/share/doc/avogadro/html/search/all_3.html
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/usr/share/doc/avogadro/html/search/all_e.html
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/usr/share/doc/avogadro/html/search/all_c.js
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/usr/share/doc/avogadro/html/search/classes_1.js
/usr/share/doc/avogadro/html/search/functions_a.js
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/usr/share/doc/avogadro/html/search/mag_sel.png
/usr/share/doc/avogadro/html/search/classes_4.js
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/usr/share/pixmaps/avogadro.xpm
/usr/share/app-install/desktop/avogadro:avogadro.desktop
/usr/share/app-install/icons/avogadro-icon.png
/usr/share/icons/Mint-Y/apps/24@2x/avogadro.png
/usr/share/icons/Mint-Y/apps/96@2x/avogadro.png
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/var/lib/dpkg/info/libavogadro2-1:amd64.shlibs
/var/lib/dpkg/info/python3-avogadro.prerm
/var/lib/dpkg/info/python3-avogadro.postinst
/var/lib/dpkg/info/libavogadro2-1:amd64.triggers
/var/lib/dpkg/info/avogadro.md5sums
/var/lib/dpkg/info/avogadro-utils.list
/var/lib/dpkg/info/python3-avogadro.md5sums
/var/lib/dpkg/info/libavogadro2-1:amd64.list
/var/lib/doc-base/documents/avogadro2
find: ‘/run/user/1000/gvfs’: Permissão negada