[Zaphod_B]

The default threadcount per core is 1 on the cluster I'm using. I can't find anything about hyperthreading in the ORCA documentation, so I am wondering whether people have seen performance increase with hyperthreading.

[Enthalpy]

Experiment it.

Not in the documentation: that's reasonable.Software doesn't need adaptation to take benefit of hyperthreading. It only needs the ability to run on several cores, and then hyperthreading will let one HT core appear like two.

Usually HT may bring 20-30% gain, provided that other resources don't limit the speed. If the L1, L2, L3 sizes slow down your application, or if the Dram throughput does, then running two tasks on the same L1, L2, L3 and Dram will bring nothing.

So depending on the core count and frequency compared with the Dram throughput and so on, and the way the software is written, HT can bring a small improvement or none. I feel logical that a software editor tells no prediction about that.