What PBC features are supported?

[leifjacobson]

Is there documentation of what PBC features are supported and what features are planned to be supported in the future?

Thank you for information help you can provide.

[awvwgk]

I'm currently working on a library backend in the tblite project, which should eventually provide PBC support in xtb and replace the currently available implementation. This will most likely be available with version 6.5.0, but I have no concrete time estimate when this will become available.

If you are looking for something more or less complete now, you can use DFTB+ which already integrates the tblite library and has decent support for various PBC features. But you have to compile DFTB+ yourself to get support for periodic xTB calculations. A stable DFTB+ release including xTB support will become available around October/November this year.

To my knowledge, tblite in DFTB+ is currently the most complete implementation of xTB with PBC support for both GFN1-xTB and GFN2-xTB.

[leifjacobson]

Thank you very much for a quick reply and for the information. If I am only interested in computing energy (and optionally gradient and stress tensor) would it be best to compile and use the tblite library directly from the github repo or to install DFTB+?

[awvwgk]

tblite is only a library backend, unless you want to implement your own simulation package or integrate xTB in an existing framework, you won't get far with this project alone. In case you indeed want to integrate xTB in another project, let me know.

Using DFTB+ with tblite gives you a pretty solid atomistic simulation framework for most PBC cases. But keep in mind that the integration in DFTB+ is still work in progress, while I'm pretty confident I got it right, there might still be some bugs. Therefore, feedback is more than welcome.

[leifjacobson]

I would plan on writing an ASE calculator for your library if the CLI is easy to use. It's sounds like you are recommending to use DFTB+ even for this purpose. Thank you for your advice. I am happy to file issues if I find any bugs.

[awvwgk]

There is an ASE calculator for xtb and for tblite already available. Feel free to share improvements to the calculators.

[leifjacobson]

great. I ran into issues using the xtb calculator which is what motivated this question. I'll checkout the tblite calculator.