Subject: Reply - Large Gaussian RWF Files

From: [email-masked]
Date: Thu, 5 Jan 1995 09:02:00 -0500

> I have a question concerning the case of large RWF-files in Gaussian 
92/DFT. > Doing analytical FREQ calculations the RWF-file grows to 
remarkable size and > sometimes becomes larger than the available diskspace 
(or the limit of the
> file-system specified by the operating system). >
> Im am working on a AIX-system and I am thinking about the possibility to 
> split the RWF-file in two files and to put them on two different
> file-systems. So my question is, if this splitting of the RWF-file is > 
possible (and HOW) ?
>
> But I would also be happy to get other comments on the possibility to > 
decrease the amount of necessary diskspace during analytical FREQ
> calculations.
> Thanx in advance
> Ch. Ehrendorfer

Common "workstation" UNIX operating systems (IBM AIX, SGI Irix 5.2 and 6.0, 
and HP UX but not DEC OSF/1 - nor Cray UNICOS or Convex) limit file system 
size to about 8-14 GB and a single file to about 2 GB.  To minimize Gaussin 
92/DFT scratch file sizes, try a combination of the keywords:

     Direct MP2=Stingy Opt=CalcHFFC Freq=NoRaman

This forces direct MP2 and direct SCF which minimizes scratch file size.  A 
system of about 165 basis functions may be accommodated within 2 GB.  Using 
"Freq" without the "NoRaman" modifier reduces the maximum problem size to 
about 150 basis functions.

     NOTE:  Do not use "Direct" redundantly, i.e., as a keyword AND as a 
     modifier for another keyword since it can "confuse" the job setup 
     routine.  For example:
     
     DON'T USE THE COMBINATION:   Direct Opt=(Direct, CalcHFFC)

Modifying the code in order to parse the scratch file(s) is a significant 
undertaking and may be unneccessary.  Relief may be forthcoming in the near 
future from the eagerly awaited next major update to Gaussian/DFT and 
manufacturers are bound to introduce changes to their OS in 95-96.  In 
other words, the modified code will be obsolete just about the time you 
modify and test it.  If you really need it now, you may consider purchasing 
or borrowing time on an alternative system, e.g., DEC OSF/1, which doesn't 
have this limitation.

Karl F. Moschner              [email-masked] 
Unilever Research U. S.