Subject: Volume keyword in Gaussian: problem

From: "Keith E. Gutowski" <gutow001^at^bama.ua.edu>
Date: Thu, 04 Nov 2004 14:26:56 -0600

I am trying to compute ionic volumes using the 'volume=tight' keyword in 
Gaussian03.  In the manual, it states for a volume calc:*

'Tight*
Requests an increased density of points for more accurate integration. 
By default, the volume is computed to an accuracy of about 10%. Use of 
this option is recommended if the computed molecular volume is needed 
more quantitatively.'

Now, when I caculate the volume of PF6- using B3LYP, DZVP2 basis set 
(opt + volume=tight), I get a strange result.  Here is the volume output 
for 6 different runs of the same input file (in cubic cm per mol):

69.815
57.036
65.763
60.465
68.880
54.854

Now, I would hope that Gaussian03 could generate better reproducibility 
that this, but am I wrong?  I have been trying to track down the source 
of this, but I am a bit stumped.  The only this I can come up with has 
to do with the error on the integrated density.  For each run (PF6- or 
whatever molecule I do), the integrated density is about 4.23D+01, while 
the error on the integrated density is about -2.75D+01.   I thought the 
error on the integrated density should be around XXXD-06.  This is 
printed out in the output along with the volume output results.

Anyone have any idea what may be going on?

Keith