ricc2 speed up with increased maxcor?

[ubelix]

Hello,

We bought reacently an Intel Xenon sytem with 8 CPU and 64 GB RAM to evaluate the possibilites of this architecutre.
In order to optimze the performance for ricc2 excited state calulations, I did several runs on 1 CPU with different amount ( 60-2000 MB) of RAM ($maxcor). Test system is a hydroxyquinoline with aug-cc-pVXZ (X=D/T) basis set (550 / 901 primitive and 316 / 667 contracted basis functions).The results are the following:

pVDZ:                                                pVTZ:
60 MB     1h 39min                          250 MB    11h 10min
125 MB   1h 29min                          500 MB    11h 00min 
500 MB   1h 25min                        1000 MB    10h 50min
1500 MB 1h 25min                        2000 MB    10h 50min

The goal is to optimize the required RAM and mount the rest as a RAM-Disk.

My questions:
1) In the manual it is writen that the amount of $maxcor has a large influence on  CPU time. Did somebody else check this relation? And what are your results?

2) Or is this test system just to small to see the speed up by $maxcor?

3) Has somebody experience with RAM-Disk? What would you expect as a speed up factor?

Regards,
Andreas

---
University of Bern

[christof.haettig]

The amount of RAM has a significant impact of on timing as long as it is small  compared to the  size of the 3-center integral arrays for virtual x occupied x auxiliary orbitals. When it reaches this size you see a "saturation". Hydroxyquinoline is for the typical size of main memory in modern machines not really a large system, in particular if you use Cs symmetry.

Christof