Subject: running G98 parallel

From: Ulrike Salzner <[email-masked]>
Date: Thu, 04 Jan 2001 10:35:21 +0200

I am using a SUN Ultrasparc with 12 processors, 3GB of memory and 21GB of
disk space to run G98. Usually I am requesting 6 processors, since there is
no speed up by adding more processors. With large jobs I am getting
messages like the one below:

  1144 basis functions     1808 primitive gaussians
   181 alpha electrons      181 beta electrons
       nuclear repulsion energy      4338.5221150204 Hartrees.
 PrsmSu:  requested number of processors reduced to:   3 ShMem   1 Linda.
   4 Symmetry operations used in ECPInt.
 ECPInt:  NShTT=   34980 NPrTT=  100852 LenC2=   14488 LenP2D=   30980.
 LDataN:  DoStor=F MaxTD1= 4 Len=   56
 LDataN:  DoStor=T MaxTD1= 4 Len=   56
Number of processors reduced to   1 by ecpmxn.
 Projected Huckel Guess.

It looks to me like the number of processors reduces because there is not
enough memory. After requesting 16 Mio words of memory, the number of
processors reduces to 3. I am not sure how far I can go, since G98 gets
very slow when more memory is requested than is available. If a normal job
would use 8 Mio words, should this be multiplied by the number of
processors? How are these machines distributing the memory? Most of the
time I am the only user on the machine but what happens if a second user
starts a job that needs a lot of memory? Also, if two jobs are running,
would it be better to use 12 processors and let the machine decide what to
do or is it better to give 6 processors to each job? Is there a rule of
thumb as to what works best? 

Thanks in advance and happy New Year,
Uli Salzner
Dr. Ulrike Salzner			e-mail:[email-masked]
Associate Professor			Tel.: 90-312-290-2122
Department of Chemistry			Fax.: 90-312-266-5097
Bilkent University
06533 Bilkent, Ankara,Turkey