Subject: CI-Density matrix summary

From: [email-masked] (Jaime E. Combariza)
Date: Tue, 25 Jul 1995 11:22:50 -0700

Many thanks to those who reply to my recent inquire.

Original question:
 
> Hi Netters: I have the following problem and will appreciate your input!
> 
> I am performing a rather large CI calculation with the option density=curr.I 
> notice that the CI run appears to be converged, with a .rwf file about 1Gbyte 
in size.  Then it looks like the 2-electron density matrix is being calculated,
> the .rwf file soars to 2Gbytes in size and the job crashes due to lack of
> disk space.  Why is the 2-electron density matrix being calculated and is 
there
> anyway to avoid the creation of this large file? The end of the output file
> is appended:
> 
> Thanks. 
> ----------
> 
>  SIZE-CONSISTENCY CORRECTION: 
>  S.C.C.=    -.18211846D+00        E(CI,SIZE)=  -.19306062986D+04
>  ***************************************************************
>  Selected functions:
>  Compute CISD 2PDM.
>  IO1PDM=    0 IOW=    0 IO2PDM=    0.
>  NGot=   2000000.
>  Frozen-core window:  NFC=  11 NFV=   0.
> File extend in NtrExt1 failed.
> 
> File extend in NtrExt1 failed: Invalid argument
> bsh: 15869 Abort: A memory image file is created as "core".
> 
> 
>From [email-masked] Fri Jul 21 13:10 MST 1995
Status: RO

Hola Jaime,

Infortunadamente solo puedo (o creo poder) responder una de tus preguntas.  La 
matriz de las integrales bielectronicas necesita ser calculada porque gaussian 
efectua el CI excitando conjuntos de electrones, de manera que necesitan 
conocerse los orbitales a-priori, de hecho, lo que se optimiza luego son los 
coeficientes de la expansion no los orbitales mismos. 

Espero haberte servido,

Albeiro.

Unfortunately I can only (or I think I can) answer one of your questions.
The two-electron integrals matrix needs to be calculated because
Gaussian carries out the CI by exciting pairs of (groups) electrons, therefore, 
the orbitals are needed apriori. In fact, what is optimized then are 
the expansion coefficients not the orbitals themselves.

+-------------------------------------------------------------------------+
|Albeiro Restrepo.  Department of Chemistry.                              |
|Carnegie-Mellon University         |                                     |
|Box 171.  Mellon Institute.        |e-mail:     [email-masked]     | 
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>From [email-masked] Sat Jul 22 06:15 MST 1995
Content-Length: 910

     Hi Jaime!

When you specify Density=Current, you instruct the program to calculate the
relaxed CI density, which requires the 2-electron density matrix. And that
indeed can become very big.

If you just want to have an indication of how CI influences e.g. the charge
distribution within the molecule, you could instead use the CI 1-particle
density for your population analysis. You need to include the options
IOP(9/30=1, 6/22=-2), which tell link 913 to calculate RhoCI and overlay 6
(the population analysis part) to analyze all available densities.
This job will run without excessive diskspace requirements.

Best wishes,

         Nico van Eikema Hommes

--
  Dr. N.J.R. van Eikema Hommes     Computer-Chemie-Centrum
  [email-masked]       Universitaet Erlangen-Nuernberg
  Phone:    +49-(0)9131-856532     Naegelsbachstr. 25
  FAX:      +49-(0)9131-856566     D-91052 Erlangen, Germany

>From [email-masked] Sun Jul 23 16:43 MST 1995
Content-Length: 495

Hmm,
if you are not using a 64bit machine then you will automatically have
trouble with single files being larger than 2Gb.

Gaussian 94 has a neet feature we have used quite often (recently) to split
the rwf up into smalle (<2Gb) chunks. It works very well, it's really neat
seeing the various rwf files filling up!!

Hope this is of some use.

Anthony P. Scott
Research Officer
Computational Chemistry Group
Research School of Chemistry
Australian National University
Canbera, ACT, Australia

>From [email-masked] Tue Jul 25 11:06 MST 1995
Content-Length: 449

Prof.  Combariza,

  In order to compute the response density for a CI calculation Gaussian
needs to evaluate the 2PDM.  This is triggered by the DENSITY=CURRENT
keyword and it does require more disk.  

  Gaussian 94 has the ability to split the RWF file into several pieces
and thus avoid the 2GB limit on a single file but I suspect that you
may be out of luck if you are still using G92 or have only 2GB available.

  Doug Fox
[email-masked]