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3:04:55 PM PDT  Fri, Jul 6th 2012 

Hello,
I would like to run some highaccuracy calculations on small molecules (two or three atoms) with up to ~10 electrons. I am considering using the CCSDTQ code available in Nwchem (I am not currently a Nwchem user). I am looking for any time/memory benchmarks for the CCSDTQ code; at the moment I am using the MRCC code by M. Kallay but, 1), it is not parallel, 2), in many situations is very, very input/output timelimited and 3), the scaling with basis set size I empirically observe is higher than what it could be in optimal cases (e.g., time scales as N^10 for a 10electron system, where N is the basis set size for a given molecule).
Thanks!




Karol Forum:Admin, Forum:Mod, NWChemDeveloper, bureaucrat, sysop


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12:08:05 PM PDT  Tue, Jul 10th 2012 

We don't have the scaling of the CCSDTQ method as a function of the systems size.
However, the scaling of the CCSDT approach was pretty consistent with its N^8 numerical complexity. Of course, the performance of the CCSDTQ implementation may be prone to the choice of the parameters which define the granularity of the code (the socalled "tilesize" parameter). This should be observed especially for the small systems.
When running the CCSDTQ calculations one should rememebr about the local memory requirements defined by the (tilesize)^8. For example, when you define "tilesize 8" in your input, you will need to store 2 object of the tilesize^8 character which is equavalent to 250 GB.
Best,
Karol



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