Molecular distortion during xtb optimization in Nightly 1.103.0

[Nyama]

I would like to express my sincere gratitude for your hard work and dedication to developing Avogadro2.

I’ve noticed an issue when performing geometry optimization using the xtb extension within Avogadro2. As shown in the attached screenshot, the molecular structure appears to distort significantly during the process.

This issue occurs in the latest nightly build (version 1.103.0 for windows11), which I downloaded on March 30, 2026.

I used the following settings for the optimization:
Optimization Level: vtight
Solvation: none
Method: GFN2-xTB

Notably, the same distortion occurs regardless of the method; I have confirmed that GFN1-xTB and GFN0-xTB also lead to the same result.

[ghutchis]

Looks a bit like it decided to make a chair cyclohexane?

What happens if you get XTB => Energy?

For an optimized benzene, it should be something like -15.8796407 Hartree

[Nyama]

I performed the calculation using GFN2-xTB, the resulting total energy was -14.460818 Hartree.

[matterhorn103]

To clarify, this is definitely with the xtb plugin using Extensions > Semi-Empirical QM (xtb) > Optimize and not with the xtb-energy plugin?

[Nyama]

Yes, I am using the xtb plugin. To be specific, I run Extensions > Semi-Empirical QM (xtb) > Optimize first, and after that, I execute Extensions > Semi-Empirical QM (xtb) > Energy.

Just for comparison, the following is the result of running Extensions > Semi-Empirical QM (xtb) > Energy after performing an initial geometry optimization with MMFF94.

[Nyama]

Sorry, I realized I didn’t fully answer your question in my previous message.

It seems that GFN2 within the Auto Optimize tool is also not functioning correctly.