Subject: Summary of Gaussian quirks

From: [email-masked] (Dave Young)
Date: Tue, 1 Feb 94 08:45:07 -0500

Hi,

	Here is the summary of messages received about Gaussian quirks.

The original posing was
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>Hi,
>
>	I'm sure many of the subscribers to this list are fluent users
>of the Gaussian XX programs.  Although these are wonderful programs,
>the number of revsions and authors has created a number of places
>where the manual is either wrong or too vague. 
>
>	I don't mean to offend the authors.  I couldn't keep on top
>of that volume of code either.
>
>	However, my question is this does anyone have a compilation
>of the various work arounds for these quirks?  Following are two
>that I have found.
>
>1.  In order to request a tighter convergence criteria, the command
>"conv=7" for 10**-7 convergence doesn't work in our version, but the
>command "iop(5/6=7)" will have the same result.
>
>2.  When doing a CISD calculation, the command "pop=no" does not give
>a complete set of natural orbitals with occupation numbers.  (By complete
>set, I desire all orbitals with non-zero occupations.)  However, if 
>you are creating a cube file from a CI calculation and have the
>commands "pop=no density=ci cubedensity=density" THEN you get the
>natural orbitals.
>
>	Please send comments directly to me [email-masked]
>and I will summarize for the list.

Replys are
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From: [email-masked] (Ivan Rossi)

Dear Dave,
	I don`t know what version of gaussian you have, but on my g92 rev b
this command work both with scf and casscf :
	scf=(conv=7)
that is equivalent to the iop(5/6=7) you reported.
I don`t use ci so i can't be helpful for the other case

	good luck
	Ivan

Ivan Rossi, Ph.D.                         |
Department of Chemistry                   |   EXPERT : (n) 
University of Minnesota                   |   someone who avoids all the 
207 Pleasant St. SE,Minneapolis, MN 55455 |   little errors, going straight
Tel. 612-624-6099                         |   towards the catastrophe   
e-mail : [email-masked]            |

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From: [email-masked] (Richard Walsh)

Dave,

The one that I would like to point out
is the description of the assignment
of additional basis functions to atoms using the MASSAGE
key word. The manual indicates that one should use the
'Center number' on page 78. The output uses the center
number inconsistently and if you have a system with dummy
atoms watch out because the output marks them as 'centers'.
If you do not get things exactly right you may end up 
with d-orbitals on hydrogen atoms! Anyway the best way to
avoid this problem is to count real atoms only and use
the GFPRINT key word to confirm that you got what you
wanted. I reported this to Doug Fox and he seemed to 
take an interest, but a fix was not in the most recent
release of the manual. I think that to some extent they
are relying on the availability of the new book to 
compensate for what is lacking in the manuals.

Richard Walsh
Minnesota Supercomputer Center
Chemistry Applications 

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From: [email-masked]

  Dr. Young,

  Your first quirk is exactly as you describe, additional options were 
added which make CONV no longer unique.  You need to use CONVER for
post-HF and SCF=CONVER=n for SCF convergence.

  Your second quirk is one I don't recognize.  I tried to duplicate it
here and did not find a difficulty.  Can you send an input which shows
the difficulty to 

[email-masked]

   In general we stand ready to address questions/problems you have with
Gaussian at that address.

Doug Fox
Director of Technical Support

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From: [email-masked]

   Dr. Young,

   For the largest part we have been able to correct the code to back up
the manual so most of the quirks are taken care of.  One feature which is
commonly missed is that you can only specify a keyword once on the route
card, i.e.

# MP2/6-31G* MP2=Stingy

will produce an MP4 calculation instead of MP2.

   On the density question I now understand the confusion.  The CI is not
formed by default for a CISD energy calculation.  This requires an additional
step to solve coupled perturbed equations and applies to any of the post-HF
methods which can produce a gradient, MP2, QCISD, CIS etc.  This step can
be fairly costly if all you require is the energy so the default is to analyze
the HF density unless you include the DENSITY keyword.  Thus the NO analysis
in you first case is of the HF density and the NO's have the all or nothing
population you observed.  In the second case you have truly analyzed the CI
density.

  My general recommendation is to use DENSITY or DENSITY=CURRENT which selects
the DENSITY of your energy keyword, if it is available, rather than using
DENSITY=CI which would fail if you did an MP2 for example.  You could also
consider adding DENSITY=CURRENT into the Default.Route file on your system
if you always want to produce the density.

   Doug Fox
   [email-masked]

				Dave Young
				[email-masked]
				youngdc@msucem