Gaussian FAQs

1. Q: Jag vill köra en beräkning med 4GB minne och 8 processorer, dvs 0.5GB per CPU. Skriver därför raden %Mem=4GB i Gaussian input filen, men får dock memory allocation error. Läste i manualen att maximum var 512MB minne per processor för g98. Stämmer detta? Vad är felet?

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   R: Följande gäller:

   (A) Monolith:
   (i) Gaussian 98: Max 512 Mbyte per CPU which corresponds to %mem=512MB in the input file, and not %mem=4GB that you have specified. In other words, in the input file it is NOT the total memory but memory per CPU that should be specified. The memory is not shared among the CPUs, so each CPU has access only to 512MB.
   (ii) Gaussian 03: Same thing as above but the limit is instead %mem=1023MB.
   (B) SGI 3800:
   The memory is shared among the CPUs and you thus specify the total amount of memory. The advantage is that you can run calcs that require large memory, but the downside is that the calc is slower on a shared memory machine (given the same speed on the processors).

   Guideline: Whenever you can run your calc with use of less then 1023MB of memory per CPU you should use Gaussian 03 on Monolith (or other shared memory resource). Only if you require larger amounts of memory should you run on SGI 3800, and you then pay the price of a slower calc.

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