OpenMolcas is real, and it’s free

Maybe you have heard about it, or maybe not. Maybe you wonder what this “OpenMolcas” thing is, if it is for real, a fake, a doubtfully legal copy, a fork, or a commercial gimmick… And in any case, what does it have to offer to your science?

Well, let’s try to get the record straight. OpenMolcas is:

  • Completely legal and approved by its authors.
  • Free of charge, free to use, open source, and free to modify and distribute under the terms of the GNU Lesser General Public License (LGPL), version 2.1
  • A major part of the current Molcas code and features.
  • Actively maintained and used for state-of-the-art research.

It is also not a fork or a sibling project, at least not currently (but, as you probably know, it is difficult to make predictions, especially about the future). This means that, as of now, OpenMolcas is the official repository for the code it contains, including your beloved SEWARD, RASSCFCASPT2, and SLAPAF (to cite a few programs you have probably used if you have ever used Molcas).

So, is Molcas 8.2 (or earlier) open source now? No, it is not. Existing Molcas versions are still covered by the license and terms under which you got them. You can, however, get most of the same code and functionality from OpenMolcas, and that is open source. Future versions of the commercial Molcas package will use the code of OpenMolcas, with possibly some modifications (as allowed by the LGPL) and additions, these additions will most likely not be open source.

What are the benefits of using OpenMolcas now? You get the latest version of the code. You can update it as soon as a new feature or bug fix appears. You can make and distribute your own modifications. However, the support you get is only what can be provided by the community of volunteer users and developers.

What are the benefits of sticking to commercial Molcas version? You get a more static version of the code, with fewer not-well-tested features. You get some codes that are not part of OpenMolcas (like EMBQ or NEMO). You can expect to get more technical support.

OpenMolcas is currently hosted on GitLab. You can find some instructions and documentation in its wiki pages. You can report problems in the “Issues” tab, but for general or specific questions regarding usage, installation, etc., please use the Molcas Forum, which is common for all Molcas flavors.

OpenMolcas repository at GitLab
Molcas homepage
Molcas Forum (also for OpenMolcas)

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