# Comparing GAMESS, OpenMOLCAS and Psi4

Over the years many open-source ab initio packages have been developed and the diversity in subroutines, methods and portability (ability to interface with other software) is quite varied for different packages. While a main distinction can be drawn between packages that focus on materials and molecular systems, within these subcategories there is still a lot of variance.

I have made a few notes about GAMESS, OpenMOLCAS, and Psi4 below, and I wonder about their validity:

• GAMESS seems to have an old academic user base and a stable code for most traditional calculations, post-HF methods (and DFT methods), solvent continuum models etc. Another good thing seems to be its ability to be interfaced MD packages like GROMACS with PLUMED(though I haven't used it).
• OpenMOLCAS has a wide range of methods implemented but, I think its not as openly available as the other packages I have mentioned here. They also have a python module pyMolcas that can be used to create workflows.
• Psi4 seems to be attractive as the source-code openly available to the community over Github and is actively being developed by a growing user-base. It has a user-friendly python module and can be easily integrated into any code/workflows. Many parts of the code seem to be written in C/C++ and features shared memory parallelization for multi-core machines.
• Welcome to the site! While this is an interesting question, I worry it might be too broad/opinion based. We did have a similar question previously that seemed to attract a lot of attention, so we will see how this one is received (or you can see that question for some of the comparison you are looking for).
– Tyberius
Aug 31, 2021 at 16:35
• Asking us to compare every single open-source quantum chemistry software is too much, and I think that asking us to compare more than two software packages is also too much. What I was able to do, was to comment on all the claims/statements you made about GAMESS, OpenMOLCAS and Psi4 while comparing them all as much as possible. I won't be comparing all three simultaneously for more aspects than what you've detailed in the first version of your post. Sep 1, 2021 at 0:49
• As pointed in the comments, this is a too broad question. In the Wiki page List of quantum chemistry and solid-state physics software we have a list of current used software in a table form where you can compare them using criteria like license type, programming language, if use MPI or OpenMPI, if compiled against GPU, etc. Also, you can check which type of system are available (molecular, periodic) and which methods are implemented (molecular dynamics, semi-empirical, HT, DFT, etc.)
– Camps
Sep 1, 2021 at 12:13
• I also would like to point out that we have recently discussed free and open source software for computational chemistry in the preprint, Free and Open Source Software for Computational Chemistry Education, chemrxiv.org/engage/chemrxiv/article-details/…. We i) define what the term "free and open source software means", ii) review a number of programs and iii) present some example calculations employing the tight-binding and density functional levels of theory. Sep 8, 2021 at 3:35

"GAMESS seems to have an old academic user base and a stable code for most traditional calculations"

GAMESS has been in development since the 1970s and split into GAMESS(US) and GAMESS(UK) in 1981, whereas MOLCAS has been in development since the 1980s and Psi4 is much newer. However, I would not focus too much on the age of the software. The first commits to the GitHub repository for PySCF were in 2014 but still it will be your first choice for certain things. The extra decades of history don't give GAMESS very much of a leg up overall against the other software packages mentioned.

"[GAMESS is good at] post-HF methods (and DFT methods),"

MOLCAS can do DFT as can Psi4. All of them can do post-HF calculations, with MOLCAS being more geared towards multi-reference methods such as CASSCF, RASSCF, GASSCF, LASSCF, CASOT2, RASPT2, etc., but still able to do coupled cluster and other things. MOLCAS also interfaces with NECI (to do FCIQMC) and QCMaquis, BLOCK, and CheMPS2 (to give 3 different options for DMRG), while Psi4 interfaces with CheMPS2 (to do DMRG) and MRCC (for arbitrary-order coupled cluster), so these programs can do a lot more of the more recently developed and closer to state-of-the-art post-SCF correlation methods.

"[GAMESS is good at] solvent continuum models etc."

MOLCAS can be used directly for solvent continuum models and Psi4 has an interface to PCMSolver for PCM (polarizable continuum model) calculations.

"Another good thing [about GAMESS] seems to be its ability to be interfaced MD packages like GROMACS with PLUMED (though I haven't used it)."

If you want something that can interface to GROMACS and PLUMED, then maybe this is the only place that you mentioned so far where GAMESS really has the other two beat, though the MOLCAS package has the DYNAMIX program which can do MD and it can bring you closer to quantum mechanical accuracy than GROMACS, via the surfacehop program and the interface to SHARC. As far as I know, Psi4 does not offer MD capabilities.

"OpenMOLCAS has a wide range of methods implemented but, I think its not as openly available as the other packages I have mentioned here. [...] Psi4 seems to be attractive as the source-code openly available to the community over Github and is actively being developed by a growing user-base."

The OpenMOLCAS source is openly available at GitLab here: I can't see why it should be considered any less "openly available" compared to the other two. GAMESS is apparently not considered "open source" and is just considered "source-available freeware" due to the way it's licensed.

"[OpenMOLCAS also has] a python module pyMolcas that can be used to create workflows. [... Psi4 also] has a user-friendly python module and can be easily integrated into any code/workflows."

While these things may be true, and you may consider them to indicate an advantage over GAMESS, I have yet to see any benefit to Python modules when doing serious quantum chemistry calculations, and I have done a lot of them. For GAMESS and MOLCAS, I would prepare an input file in VI and then run the software with scheduler via a submissions script. I can imagine a Python interface providing me with some benefits, and also some problems (in addition to those problems, I actually never managed to run a calculation in Psi4 because of its relationship to Python and the difficulties I had with installing it using the documentation's recommended process involving Anaconda and components which required Python versions higher than what I had available at the time).

"Many parts of the [Psi4] code seem to be written in C/C++ and features shared memory parallelization for multi-core machines."

Any quantum chemistry software worth discussing, has parallelization implemented for multi-core machines. GAMESS and MOLCAS are written in FORTRAN, which is specifically designed for scientific computing and number crunching, whereas C/C++ were designed for more general purposes, such as for operating systems, computer games, etc. FORTRAN is arguably much easier to learn, and large FORTRAN software packages like GAMESS and OpenMOLCAS tend to be easier to install because they don't have dependencies like BOOST and Eigen which are needed for C/C++ programs to do high-performance calculations (I mentioned that I've never been able to install Psi4 because of some Python issues, but I've also struggled with installing other C/C++ software due to the delicacies associated with BOOST and Eigen versions). See this: What is a good programming language for matter modeling?

• I do not know what caused with your PSI4 installation. But for a person with below average linux knowledge, PSI4 installation using conda or precompiled binary is pretty easy. I think you were trying with source package. Sep 7, 2021 at 6:55
• It was a while ago, things may habe changed. Sep 7, 2021 at 12:55
• Minor note - you forgot Firefly in the GAMESS projects. Sep 16, 2021 at 20:04