[quadruplebond]

I don’t use Fortran but I agree as of today and probably post 90 Fortran is nice enough but people moved to c++ for things like polymorphism and templates and pointers among other things. You could probably also rewrite nwchemex in Modern Fortran just fine. I’ll give you one example of why C++ might be easier though. Next gen linear algebra libraries are being written in c/c++ such as elemental and dplasma also Cyclopes tensor framework and probably others. When the libraries you want to use are in c/c++ the that can be the easiest path forward.