Subject: IRC problems in Gaussian 94 occur also with OPT=QST2 option

From: Han Zuilhof <[email-masked]>
Date: Wed, 17 Jan 1996 15:23:16 -0500 (EST)

Dear CLL netters,

Recently a problem regarding IRC calculations in Gaussian 94 was brought 
up. Mike Frisch clarified the discussion by stating that LST does in 
itself not yield a real transition state, and that the new OPT=QST2 
routine should be used.

However, this does not solve the 'out of range' error! I've bumped into 
it several times myself, using the OPT=QST2 method (and confirming 
frequencies) in G94 (versions B3 and C3). A condensed file example of input 
and output is given at the end of this letter. I hope that further discussion 
of this problem on the CCL net will clarify this situation. IRC is 
conceptually a very nice tool, but I've found it in several cases to be 
troublesome or even impossible to get it to work within G94. The 'out of 
range' problem is just one of them. It would be helpful to find out 
precisely a) what this error means, and -more importantly- b) how one can 
get around it. 
Another problem I bumped into is that the IRC on a TS (as optimized with 
OPT=QST2 and checked with FREQ) simply doesn't "leave the area" on the 
potential energy surface around the TS, and yields after 2-5 steps a 
geometry nearly identical to the TS as one of its minima. 
Here a 'way around' is sometimes to start the IRC from a geometry close 
to the TS along a 'self-chosen' reaction coordinate (choice base on 
e.g the character of the imaginary frequency), but this 
trick is both somewhat arbitrary and also not-infallable. If someone 
knows how to deal with this problem, I would be very glad!

Thanks in advance to anyone who can help,

Han Zuilhof

--------------------------------------------------------------------------
Gaussian 94 .com input file and excerpt of .log output file:

%chk=c110507for
#p irc=(maxpoints=100,rcfc,forward) geom=check guess=read uhf/6-31G(d)

c110507for;forward IRC TS H2O + 2-Me-butane catrad at 2-pos;

1,2

-----------------------------------------------------------------------
 ***************************************
 Gaussian 94:  SGI-G94RevC.3 26-Sep-1995
               13-Jan-1996
 ***************************************
 %chk=c110507for
 ----------------------------------------------------------------------
 #p irc=(maxpoints=100,rcfc,forward) geom=check guess=read uhf/6-31G(d)
 ----------------------------------------------------------------------
 c110507for;forward IRC TS H2O + 2-Me-butane catrad at 2-pos;
 ------------------------------------------------------------
 Redundant internal coordinates taken from checkpointfile:
 c110507for.chk

(stuff deleted)

Route:  #P FREQ=NORAMAN GUESS=READ GEOM=CHECK UHF/6-31G*
 Cartesian force constants read from checkpoint file:

(stuff deleted)

(Enter /usr/local/g94/l716.exe)
 OPERATION ON FILE OUT OF RANGE.
 FILEIO: IOPER= 2 IFILNO(1)=-10511 LEN=    4559 IPOS=       2 Q=        
27356885
6

 dumping /fiocom/, unit = 1 nfiles = 69 sizext =    524288 winblk =   64
                   defal = T lstwrd =   4099136

 number         0        0        0        0        0        0        0
 base      151424   116480    46656  1128448  1187456  1093376   122880
 end       152704   118720    46720  1138304  3574784  1107328   122944
 end1      152704   118720    46720  1138304  3574784  1107328   122944
 wr pntr   151424   116480    46656  1128448  1187456  1093376   122880
 rd pntr   151424   116480    46656  1128448  1187456  1093376   122880

 (stuff deleted)

 Error termination in NtrErr:
 NtrErr called from FileIO.

******************************************************************************
**   Dr. Han Zuilhof           **  e-mail: [email-masked]  **
**   Department of Chemistry   **                                           **
**   University of Rochester   **                                           **
**   Rochester, NY, 14627      **  Fax:   (716) 473-6889                    **
**   USA                       **  Voice: (716) 275-2219                    **
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**                        "Excite a photochemist!"                          **
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