Can you explain the difference between what the two task types are doing? I'm curious as to what accounts for the significant difference in duration between them.

NWChem is for small molecules (9 heavy atoms). Most of them are generated by an AI method and the purpose is to explore the limit of chemistry. the AI method objectives are a combination of diversity and similiarity to known datasets. it implies generation of unstable molecules, thus a certain amount of invalid results. These invalid results are very useful to build another AI method able to generate bigger stable molecules.

NWChem long is for large molecules and more directed towards high-throughput screening (HTS). At the moment, we simulate molecules for applications in energy (photovoltaic) and medecine (phototherapy). Computation are very long and stability is also a concern.

...stability is also a concern.

Half of my NWChem Longs are Validation Inconclusive and a fifth are Invalid.
Any hope this will improve???

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I've reported my results in Number Crunching, with a typo in the name.
Tullio

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Unlike nwchem, nwchem longs are real molecules. Unfortunately, it is difficult to improve success rate of such computations...