Subject: 16GB file problem in Gaussian

From: Alessandro Ponti <alessandro.ponti-.at.-istm.cnr.it>
Date: Fri, 27 Jun 2003 14:25:38 +0200

Dear All,
recently I met with the problem that the maximum total RWF file length in 
Gaussian98 is 16GB. (NB: I'm not referring to the maxiumum file length allowed 
by your OS; such problem is solved by splitting the RWF into several small 
files). I met the 16GB problem while trying MP2 frequency, MP4 energy, and QCISD 
energy calculations. Apparently, Gaussian98 cannot deal with more than 16GB disk 
space, eg when you set MaxDisk=17GB. Looking at the route section, IOp(8/27) 
("maximum amount of dik to use" in the four-index transformation) is negative 
and equal to -1GB (recall that IOp(8/27) is expressed in Words). Here's a small 
table of my experiments

MaxDisk   : 1 2 ... 15  16  17 ... 31 32 33 ...
IOp(8/27) : 1 2 ... 15 -16 -15 ... -1  0  1 ...

Perusing G98 manuals and source files was useless. After searching in the net, 
it seems that the 16GB problem is related to Gaussian98 addressing by 32-bit 
integers. At 
http://www.ccl.net/ASC/PET/CCM/skeleton/software/gaussian/gaussian-tips.html
I found a brief text claiming this problem can be circumvented, at least partially:
"The second limit has a less satisfactory workaround. Scratch data stored in the 
read-write file can be diverted into a separate file with the option

%usescr

while this does not evenly balance the usage it does allow specification of 32 
GB of storage and depending on the type of calculation more or less complete 
utilization of this whole amount."
However I did not really understand what it means.

Does anyone knows how to overcome the 16GB limit? Has anyone information about 
this problem? Any little piece of information might be a precious clue to us.

I thank you all in advance for any help.
Bye

Alessandro
-- 
******** NEW TELEPHONE NUMBER AND EMAIL ADDRESS ********
+------------------------------------------------------+
|  Dr. Alessandro Ponti                                |
|                                                      |
| Consiglio Nazionale delle Ricerche                   |
| Istituto di Scienze e Tecnologie Molecolari          |
|                                                      |
| via Camillo Golgi 19  | Tel   +39 02 5031 4280       |
| I-20133 Milano        | Fax   +39 02 5031 4300       |
| ITALY                 | email a.ponti.-at-.istm.cnr.it    |
|                       | www   www.istm.cnr.it/~ponti |
+------------------------------------------------------+