Subject: Re: CCL:Re:NWChem

From: Gregory Shamov <[email-masked]>
Date: Tue, 5 Nov 2002 23:19:35 +0300

Hello uccatvm,

Sunday, November 3, 2002, 4:55:09 PM, you wrote:

u> It is true that NWChem is slower than Gaussian on a single processor.

Much much slower.

u>  However, the main advantage of NWChem is its, indeed, excellent
u> scalability, and that holds for small as well as large clusters,
u> for shared-memory as well as distributed-memory machines.
[skip]
u> As I mentioned above, as I do not have any experience with Gamess,
u> I cannot  comment on its performance on small clusters, but in my
u> experience NWChem  does scale very nicely on these machines.

NWChem scalability is not an advantage for small clusters, because
speed is sacrificed to it. What do you need from clusters -- smaller
wallclock times or better scalability? As I said, scalability of
NWChem is useful for large clusters only. 

Perhaps you better should try Gamess and double your calculation
speeds (not speedups).

u> In addition, because of its distributed data approach, it can
u> handle larger calculations on parallel machines where programs that
u> use a replicated-data approach

Yes, it is true. NWChem must be good for Grand Challenge tasks running
on Grand Size Clusters. (A propos, Gamess uses this DDI-thing for MP2
energies and gradients too).

u> This is very strange, because I don't see that behaviour. I get
u> very nice  speedups with NWChem, on small as well as larger
u> clusters. Running on 2  or 4 nodes, I generally get speedups of
u> close to 2 and 4 on different  architectures (that's for running ab
u> initio - like SCF and MP2 -  calculations). Even on Linux clusters
u> connected by only fast ethernet  I get speedups of 6.65 for running
u> on 4 dual processors. 

Today I have no working NWChem installation (because I have deleted it
year ago), but I will look for my old test results soon.

I have used (well, not used, just tested) NWChem on Linux clusters on
Alphas and PCs, with Fast and Gigabit Ethernet.

-- 
Best regards,
 Gregory                            mailto:[email-masked]