[Pw_forum] time requirement

Paolo Giannozzi giannozz at nest.sns.it
Mon Jan 7 09:35:21 CET 2008

On Jan 7, 2008, at 6:38 , Rudra Banerjee wrote:

> my machine(desktop,linux) is 3 GB ram, but yet it is using more space
> (SWAP) and giving only 2-3 iteration per day.
> is my input somewhat inefficient? pl. let me suggest any  
> improvement if possible

assuming that you cannot reduce the size cell and the cutoff:
- do not calculate stress if you do not need to: it is expensive
- conv_thr = 1.0d-10 is quite high, 1.0d-8 should be enough
- is your system an isolated system? then use
K_POINTS gamma :
   it will use k=0 only (which is all you need for an isolated system)
   and exploit various tricks to reduce memory usage
- setting option "diago_david_ndim" to the minimum (2) and "mixing_ndim"
   to a smaller value (4) reduces memory usage, but may increase CPU  
- using diagonalization='cg' will also reduce memory usage, but it will
   increase CPU time by a sizable amount

Paolo Giannozzi, Dept of Physics, University of Udine
via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222

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