[Wien] help on computer for WIEN2k calculation

[Peter Blaha]

Hi,
The answer to your question is not so simple and depends a lot on:

is this dedicated to WIEN2k or will other software also have a large
fraction of cpu time ?
how much money do you have in total (there's a big difference between
5000 and 100000 or more $) ?
For which WIEN2k tasks do you plan (system size) ?

For many tasks AMD and Intel cpus are fairly "equal", i.e. they perform
similar within 10-20 % and either one may be faster for a particular case.

For WIEN2k this is quite different ! Due to the dominant time of 
diagonalization and the high efficiency of Intel cpus for this task,
an Intel cpu is significantly faster than AMD (160 vs 260 seconds, see 
benchmarks) !!

dual core is now the way to go (very cheap (almost) doubling of performance),
support by BLAS-libraries, similar for AMD and Intel.


for "regular" WIEN2k cases (system size usually below 50 atoms; maximum of
100 atoms/unit cell) and a "limited" budget (a few k$):

I'd go for a couple of Intel P4 D-830 or 840 with Gbit-network and SATA
disks.

I'd use Xeons only for really "big" machines (and more money). Furthermore
at the moment the dual-core Xeons run only at 2.8GHzt, but
new processors (with 65 nm technology) are expected soon, so I'd almost
"wait" (if possible).

I'd use AMD only for even bigger machines and big "cases". In these cases
you may want to use the mpi-parallel version and thus you need a fast network 
(Infiniband), which is quite expensive. In this case (and ONLY in this case)
it pays off to buy these multi-cpu machines (like like a two or four socket -
dual-core AMD Opteron).


memory: again it depends on the cases you want to study. Minimum is 2 GB,
when you plan for bigger cases, buy 4 GB per "socket".

Regards

> Dear users,
>     We are planning to buy a new computer for WIEN2K calculation.  Three
> kinds of CPU, AMD Athlon 64 X2 3800+(dual core), Pentium D 830(dual core) or
> double Xeon 2.8G are considered . But we are not sure which one is better
> for WIEN2K. It seems that Intel CPU is better from the benchmark on the
> WIEN2k website. Does dual-core CPU is better than double CPU(one core)?
>  We greatly appreciate that somebody can give us some suggestions about
> CPU,memory and so on.
> 
> Best regards.
> 
> Zeming
> 


                                      P.Blaha
--------------------------------------------------------------------------
Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-1-58801-15671             FAX: +43-1-58801-15698
Email: blaha at theochem.tuwien.ac.at    WWW: http://info.tuwien.ac.at/theochem/
--------------------------------------------------------------------------