ENCCS is expanding its software support work for chemistry to also include OpenMolcas.

OpenMolcas is a molecular electronic structure package focused on multiconfigurational methods. The program can compute molecular ground- and excited-state energies with state-of-the-art accuracy for many complex electronic structure problems. This accuracy comes at an increased computational cost: access to and efficient use of high-performance computing clusters is essential for comprehensive multiconfigurational studies. OpenMolcas is open source (LGPL licensed) with an open development workflow. It is a large code, written in a mix of languages: primarily Fortran (77 and 90) with some C and external modules in C++.

OpenMolcas has a large, international user base. It is among one of the most used software packages for multiconfigurational quantum chemistry, in Europe and around the world. The code can exploit homogeneous cluster architectures, with parallelization achieved mainly through global arrays (GA) and message passing (MPI). Shared-memory parallelism is used implicitly through linking to threaded BLAS and LAPACK.

In the coming year, we plan to work with OpenMolcas to refurbish and add functionality, while at the same time studying the performance of the code and identify where to improve. In particular, we plan to:

• Perform scaling and scalability studies on EuroHPC-JU systems.
• Overhaul the continuum solvation functionality in OpenMolcas, by interfacing with a newly developed library.
• Develop an interface with the TREX-IO library, maintained by TREX CoE, for quantum chemical input-output.