Subject: Re: CCL:NWChem

From: Gregory Shamov <[email-masked]>
Date: Sun, 3 Nov 2002 09:21:29 +0300

Hello Dmitry,

Sunday, November 3, 2002, 3:09:16 AM, you wrote:

DR> Hi.

DR> Does anybody use NVChem?

I have tryed to use NWChem 4.0 and 4.01.

DR> Does it have any advantages over Gamess-US? 

NO.

The main advantage of Gamess (Gaussian, Jaguar, Qchem, ...) over
NWChem is that Gamess, in general, is stable, and NWChem, in general,
is not. 

And there are some minor disadvantages of NWChem. First, it slow. Very
slow. At single CPU it is about 2-4 times slower than Gamess. The
NWChem team says it is because NWChem is designed to be very
scalable code to use on hundreds and thousands CPUs. I believe it is
true, but for commonly used small clusters (8-16 CPUs) Gamess
outperforms NWChem.

Moreover, NWChem (at least in some cases) running on the small cluster
(say, 8 CPUs) gives no normal speedup painting! I.e., wall times for
the same task are not smoothly decreasing with increasing CPU number,
but are changing randomly. Perhaps in the case on 1000 CPUs cluster
+\- 8 CPUs means nothing, aha, aha, but for small cluster every CPU
means a lot. :-) The same task calculated with Gamess on the same
cluster scales properly.

There are a lot of methods implemented in NWChem: DFT, CCSD, CPMD,
classical MD, etc. But DFT (both grid-based and grid-free) and CCSD
methods are implemented in the latest versions of Gamess too, it is
possible to integrate Tinker with Gamess to do QM\MM and MD
calculations, and there is standalone free and cool CPMD program.

So i think you better use these codes unless you have 1000CPUs
cluster.

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