Subject: CASMP2(10,10) Problems and Answers

From: Keith Kuwata <[email-masked]>
Date: Thu, 15 Jul 1999 19:18:02 -0700 (PDT)

Hi CCLers,

I apologize for the huge (2 month) delay in summarizing
answers.  

_________________________________________________________________

Here was my original problem:

I have converged CASSCF(10,10)/6-31G(d,p) wave functions (95 basis
function total).  I have been unable to obtain single-point
MP2 corrections (using the keyword MP2=full) 
with either Gaussian 94 or Gaussian 98.

G94 has failed on both an SP2 cluster and the NCSA HP Exemplar
If I use the keyword iop(4/43=1), the job crashes before the CAS begins
with the error message "OPERATION ON FILE OUT OF RANGE"
If I omit this keyword, the job crashes with a "Segmentation
Fault" right after the route information prints.  This happens
even when 4 GB of RAM are allotted.

With G98 on the Exeplar, CASSCF(10,10) runs successfully with the 
battery of additional keywords posted by Wolfgang Roth last month:
  casscf(10,10,nofulldiag) iop(5/6=8) iop(4/46=1,5/39=000001)
  iop(5/16=1)

Upon adding the keyword mp2=full, G98 at least doesn't crash
(unlike G94).  However, in the MP2 routine, all the configurations
are skipped and there is zero MP2 correction to the CASSCF energy.

I know that CASPT2 is arguably better, and I am pursuing those
calculations as well.  But it would be very useful to have CASMP2
(10,10) energies for comparison.  If anyone knows how to get this
to run on either G94 or G98, that'd be great.

______________________________________________________________

Here's what solved the problem:

1) The insight that I was running out of scratch disk space:

Your input deck looks fine and the job runs if you reduce the active space
so I think it must be a size problem. Does the job run without the
'mp2=full' option?  The MP2 will need a lot of memory (actually I'd be
surprised if it runs in G94 at all), whereas the CASSCF needs a lot of
disk space but not so much memory. My guess is that the scratch files were
probably not written properly as the job ran out of disk space. The only
machine I ran my CAS(10,10) jobs on was NCSA which had a lot of disk
space. Do you have access to a machine with a lot of disk space? The CAS
should certainly run providing it has enough disk space - I don't think
there is a problem with the code or your input deck.  The MP2 I suspect is
much too large to run with G94 - perhaps it will run with G98.

Sarah Wilsey <[email-masked]>

_________________________________________________________________

2) And that CASMP2 even on G98 can run out of disk space easily:

Gaussian evaluates MP2 corrections only for configurations having 
coefficients (in localized orbital basis) higher that a selected threshold.
The problem in your case appears because all configurations
have coefficients lower than the threshold.

"Dr. Paolo Celani" <[email-masked]>

_______________________________________________________________

3) The fix for the problem, also from Dr. Celani:

A IOP in GAUSSIAN is set with the syntax

IOP( link_number / option_number = option_value )

link_number   = 5 in your case because you want to set an option of l510
option_number = 52 this is the specific option you want to set
option_value  = 0,1,2, .... any integer number

The threshold is set by default to 0.01 (option_value=0) which means that only
configurations having CI coefficients >= 0.01 (in absolute value) 
will be considered for the successive correlation calculation.
If you want to set a threshold to 0.001, you must add a card like

iop(5/52=1000)

For a threshold equal to 0.0025, the card is iop(5/52=400).
In general (as said by the formula), the threshold for coefficients will be
set to a value equal to the inverse of the value of the option 52 or it is
set to 0.01 if option_value=0.

Keep in mind that you might get different answers using different cutoffs. 

"Dr. Paolo Celani" <[email-masked]>

_______________________________________________________________

Of course, this trick is never mentioned in the Gaussian
documentation.  Nor did I get any hint from Gaussian in my
e-mail communication with them.  In that vein, I received 
this comment:

> P.S. [Needless to say], Gaussian has failed to respond to my three
> requests for help.
> 

We see this too often on CCL.  I do not mind people asking for help, 
but the point is they should be getting help from Gaussian.  They 
don't, so they turn to CCL, get the answer, and Gaussian is off the 
hook.  Perhaps Jan and all the responders should collect a fee from 
Gaussian for doing their work for them?  Or maybe users should 
abandon Gaussian and go with competitors who provide some real 
customer support.  Other opinions, suggestions welcome.

Jaime Martell <[email-masked]>

_______________________________________________________________

The article in this week's (12 July 1999) C&E News provides 
further insights into Gaussian, Inc.

Thanks much to everyone who responded,

Keith Kuwata