Moving the Effective Fragment Molecular Orbital method towards exascale*

Steep computational scaling and significant memory requirements of conventional electronic structure methods both limit the size of systems that can be described and hinder transitioning towards exascale computing. One of the ways to overcome these problems is to use fragmentation approaches. Our approach of choice is the Effective Fragment Molecular Orbitals (EFMO) method, which combines advantages of the Fragment Molecular Orbital (FMO) and the Effective Fragment Potential (EFP) methods. The current implementation in the GAMESS program package, however, is not optimized nor fully parallelized.

In this study, a major effort is related to optimizing the bottleneck step of generating EFP parameters, called MAKEFP, which needs to be repeated for every new fragment geometry in the EFMO method. In addition, improvements implemented in other parts of the EFMO code include increasing accessible system sizes. The resulting performance is demonstrated using a ~1700-atoms piece of a mesoporous silica nanoparticle (MSN), which was inaccessible in the original implementation.