CCL: computer for high-level QC calculations

 Sent to CCL by: "Jeff  Hammond" [jeff.science-*-gmail.com]
 Pablo,
 An SGI Altix 4700 is a great machine to run NWChem on, as the code runs
 extremely well on Itanium processors and will utilize every last drop of shared
 memory if you ask it to.
 GAMESS, PQS and Aces II (MAB) utilize disk for large CC calculations and were
 designed to run on machines with more modest interconnects.  That is not to say
 that they won't benefit from a higher network bandwidth and lower latency, but I
 don't think you'll get your money's worth.  For these codes, you're probably
 better off buying a machine like the ones the developers demonstrate those codes
 on, which is a Beowulf cluster with striped SCSI disk arrays and channel-bonded
 Ethernet (approximately).
 Aces 3 is quite new, but should run well on an SGI Altix, assuming it is
 supported.  The Aces 3 design paradigm permits platform-specific optimization
 which might be able to exploit the special features of the Altix.
 You can refer to the following articles which discuss the relative performance
 of various codes in parallel.  Each paper notes the hardware that the code was
 tested and timed on.
 Aces II (MAB) - J. Chem. Theory Comput., 4 (1), 64 -74, 2008 -
 http://pubs.acs.org/cgi-bin/abstract.cgi/jctcce/2008/4/i01/abs/ct700152c.html
 GAMESS - J. Chem. Theory Comput., 3 (4), 1312 -1328, 2007 -
 http://pubs.acs.org/cgi-bin/abstract.cgi/jctcce/2007/3/i04/abs/ct600366k.html
 PQS - J. Chem. Theory Comput., 3 (4), 1368 -1377, 2007 -
 http://pubs.acs.org/cgi-bin/abstract.cgi/jctcce/2007/3/i04/abs/ct700048u.html
 Aces 3 (QTP) J. Chem. Phys. 128, 194104 (2008) - http://link.aip.org/link/?JCPSA6/128/194104/1
 NWChem (old CC code) J. Phys. Chem. A, 109 (31), 6934 -6938, 2005 -
 http://pubs.acs.org/cgi-bin/abstract.cgi/jpcafh/2005/109/i31/abs/jp044564r.html
 NWChem (TCE) J. Chem. Phys. 127, 144105 (2007) - http://link.aip.org/link/?JCP/127/144105
 (The timing data in this paper is already obsolete, but the scalability is
 representative.)
 I am not aware of any reason why Itanium would be an issue.  The Intel compilers
 do a fine job of generating fast code and this chip is the best available for
 DGEMM, which is the fundamental kernel for coupled-cluster codes.
 Best,
 Jeff