Re: How much memory?


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Posted by Valera Veryazov on April 30, 2008 at 20:59:21:

In Reply to: Re: How much memory? posted by Ignacio on April 30, 2008 at 19:29:43:

> What I would like is a way to estimate, in advance, that the 12GB are not "enough" for the calculation with basis set B.

well, if 12Gb is not "enough" - what can you do? If you increase MOLCASMEM to say 15Gb there is risk (since some parts of molcas can allocate ALL free (at the moment) memory allowed by MOLCASMEM) that you will take from OS almost everything - and I/O will extremely inefficient. So, this is not advisable to make MOLCASMEM higher than 75% of RAM.
From other hand, this is not a good idea to make MOLCASMEM too small.
First, some arrays must be allocated - and you probably seen some messages, that MOLCASMEM should be increased (Note, that the code can make only a provisional guess how much you will need).
Also, if you set MOLCASMEM just above this 'must have' value - some algorithms will be switch to 'out of core' mode. with obvious expenses..

/Valera



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