Subject: Summary: Potential Enery Scan in G94

From: "C.F. Matta" <[email-masked]>
Date: Sun, 5 Jul 1998 17:20:09 -0400 (EDT)

Dear CCLers,

  I would like to thank Doctors Douglas Fox, Darko Babic, and Stefan Fau
for their help in solving my problems with Potential Energy Surface (PES)
scan in Gaussian94.  The complete answer is really a combination of the 3
replies.. and the job is currently running as I am writing.

  This summary comprizes the following sections:
      1. The problem as posted 
      2. The complete solution that worked (actually a combination of the 
         three responses)
      3. The individual responses of Douglas Fox, Darko Babic, and Stefan
         Fau

                             Cherif Matta
                             Graduate student
                             Chemistry Dept.
                             McMaster University
                             Hamilton, Ontario

==================================================
1. THE ORIGINAL PROBLEM
===================================================

 I am trying to perform a potential energy surface scan using Gaussian94.
It is the first time I try this option and the manual is not very clear as
to how should one handle the following situation:

1. I optimized the z-matrix keeping three torsion angles as constants
   (froozen).

2. I want to use the optimized geometry from the check point file as an
   input to the potential energy scan BUT would like to keep ONE of the
   previously frozen torsions as it is, while perform the PES on the TWO
   others. Below, please find my input (com) file and the error message I
   get in my (log) file.

                      INPUT (COM) FILE
# rhf/3-21g scan  opt=(AddRedundant, readfc) scf=direct
scf=tight geom=modify geom=(noangle, nodistance)

Diacetyl glycoluril model (with demethylated Nitrogens), June 1998.

0 1

tor5      180.0  11 30.0
tor17    180.0  11 30.0

                ERROR MESSAGE IN THE LOG FILE

----------------------------------------------------------------------
 # rhf/3-21g* scan opt=(AddRedundant, readfc) scf=direct 6d scf=tight g
 eom=modify geom=(noangle, nodistance)
 ----------------------------------------------------------------------
 Unrecognized IType=10.
Error termination via Lnk1e in /usr/people/gauss/g94/l1.exe.
 Job cpu time:  0 days  0 hours  0 minutes  0.6 seconds.
 File lengths (MBytes):  RWF=   44 Int=    0 D2E=    0 Chk=    5 Scr=    1

==================================================
2. THE COMPLETE SOLUTION
===================================================

# rhf/3-21g* opt=(Z-matrix, ReadFC)  geom=(modify, noangle, nodistance)

Diacetyl model (with demethylated Nitrogens), June 1998.

0 1

8 7 2 3        180.0 S 11 30.0
16 18 19 20     180.0 S 11 30.0

==================================================
3. INDIVIDUAL RESPONSES
===================================================

DOUGLAS FOX
============

From: Doug Fox <[email-masked]>

   Prof. Matta,

   The immediate problem I note is that you are trying to mix Z-matrix
internals with redundant internals.  Second, you have both SCAN and OPT
on the same route.  Third, you have used the keyword GEOM twice and
should group all three options with one instance of GEOM.  Similarly you
should group the options for SCF or omit them as SCF=Direct is default and
SCF=Tight is default for an optimization.

   What I would recommend in such a case is that stick with a Z-matrix
description since you have previously optimized this way.  You then need
to decide if you want to do a SCAN or an OPT.  A relaxed potential energy
scan with one fixed dihedral and the other two fixed to a series of values

but all other variables optimized can be done with

#  .... OPT=(Z-matrix,ReadFC) Geom=(Modify,NoAng,NoDist)

Relaxed PES

0 1

tor5      180.0  S 11 30.0
tor17    180.0  S 11 30.0

Slightly cheaper would be a simple scan but this does not allow the rest
of the structure to relax.  Here just use SCAN and the input you have.

Douglas J. Fox
  Director of Technical Support
  [email-masked]

DARKO BABIC
============

From: Darko Babic <[email-masked]>

        Hi!

        I think that Gaussian can not combine PES SCAN and PARTIAL
optimiza-
tion.  So for each point on a grid of fixed parameters (you have just one
- the frozen torsional angle) I prepare a (more or less) separate job with
explicit constant and variable parameters, and with POpt instead of Opt.

        Maybe one could use the "Modify" option for changing the geometry
>from the previous job, but this would be a sequence of separate jobs any-
way.

        If you need more information or if there is another solution,
please,
let me know.

                                        Sincerely,
                                                                Darko
Babic

STEPHAN FAU
============

From: Stefan Fau <[email-masked]>
Reply-To: [email-masked]

Hi Cherif,

the correct notation for stepped dihedral angles is:

N1 N2 N3 N4 [value, not neccessary with geom=modify] s steps stepsize

N is the number of an atom in the geometry specification, not counting
dummies.

In your input, you used torsN to specify some dihedrals, which only
works in conjunction with a z-matrix. You also forgot the s between
value and the steps parameter.

Regards,
         Stefan

---------------------------------------------------
Stefan Fau                [email-masked]
FB Chemie der Philipps-Universitaet Marburg
Hans-Meerwein-Str.
D-35032 Marburg