Subject: Converge problem in the optimization on G94

From: Seiji Mori <[email-masked]>
Date: Tue, 25 Jul 95 13:43:47 JST

Dear Netters;

 I use the gaussian 92 and g94 programs. I have a problem about the geometry
 optimization
 and frequency analysis.
 After the geometry optimization completed ,I
performed the frequency calculation analysis. However, from the output of frequency
analysis ,
 sometimes Optimization is not completed because values about displacement
 exceed the thresholds. How should I resolved it and wolud you tell me your
thought about this problem ?

   I show the following example, for the same structure,
---
 from the optimization--
 -------------------------------------------------------------------
 Center     Atomic                   Forces (Hartrees/Bohr)
 Number     Number              X              Y              Z
 -------------------------------------------------------------------
    1          8           -.000000354     .000000167    -.000003124
    2          6            .000000252    -.000001602    -.000002878
    3          1            .000000565     .000001205     .000000257
    4          6           -.000000992    -.000003086     .000002942
    5          3            .000000015    -.000001105     .000001460
    6          1           -.000000899    -.000000567    -.000001878
    7          1            .000001063     .000000184     .000000899
    8          1           -.000001582     .000000683    -.000000353
    9          6            .000003439     .000004875     .000000566
   10          1           -.000003443    -.000001508     .000000881
   11          1            .000002364     .000002099     .000001358
   12          8           -.000000689    -.000001094     .000002595
   13          6            .000000214     .000000425    -.000003147
   14          1            .000000368     .000000556     .000000653
   15          1           -.000000386     .000000051     .000001280
   16          1            .000001086    -.000000075     .000000193
   17          3           -.000005487    -.000001164     .000001193
   18          6            .000006121    -.000009568    -.000012355
   19          1            .000003418     .000007083     .000002534
   20          1           -.000008932    -.000002296    -.000001040
   21          1            .000003860     .000004737     .000007963
 -------------------------------------------------------------------
 Cartesian Forces:  Max      .000012355 RMS      .000003356
 Internal  Forces:  Max      .000008263 RMS      .000002536

         Item               Value     Threshold  Converged?
 Maximum Force             .000008      .000450     YES
 RMS     Force             .000003      .000300     YES
 Maximum Displacement      .001537      .001800     YES
 RMS     Displacement      .000439      .001200     YES

from the frequency analysis---
 -------------------------------------------------------------------
 Center     Atomic                   Forces (Hartrees/Bohr)
 Number     Number              X              Y              Z
 -------------------------------------------------------------------
    1          8           -.000000351     .000000168    -.000003123
    2          6            .000000251    -.000001603    -.000002879
    3          1            .000000564     .000001202     .000000257
    4          6           -.000000992    -.000003084     .000002944
    5          3            .000000015    -.000001106     .000001461
    6          1           -.000000899    -.000000567    -.000001879
    7          1            .000001062     .000000184     .000000899
    8          1           -.000001581     .000000682    -.000000354
    9          6            .000003440     .000004876     .000000569
   10          1           -.000003443    -.000001508     .000000881
   11          1            .000002365     .000002099     .000001359
   12          8           -.000000691    -.000001095     .000002592
   13          6            .000000211     .000000432    -.000003151
   14          1            .000000365     .000000554     .000000654
   15          1           -.000000385     .000000052     .000001284
   16          1            .000001089    -.000000078     .000000192
   17          3           -.000005487    -.000001164     .000001193
   18          6            .000006119    -.000009568    -.000012354
   19          1            .000003418     .000007083     .000002533
   20          1           -.000008932    -.000002296    -.000001040
   21          1            .000003861     .000004737     .000007963
 -------------------------------------------------------------------
 Cartesian Forces:  Max      .000012354 RMS      .000003356
 Internal  Forces:  Max      .000008262 RMS      .000002536

         Item               Value     Threshold  Converged?
 Maximum Force             .000008      .000450     YES
 RMS     Force             .000003      .000300     YES
 Maximum Displacement      .001946      .001800     NO
 RMS     Displacement      .000524      .001200     YES
----

 Sincerely,
 Seiji Mori
 Department of Chemistry
 The University of TOkyo
 email:[email-masked]

---

From: Craig Wilson <[email-masked]>
Date: Tue, 25 Jul 95 10:36:19 BST

>  email:[email-masked]

After your initial optimization, do a further optimization with the keyword

Opt=Tight

This will reduce the displacements and forces still further, and should allow
your frequency job to run correctly

Hope this helps,

Craig

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* Craig Wilson                              e-mail: [email-masked]   *
* Dept. of Chemistry                                                          *
* University of Warwick                                                       *
* COVENTRY                           Phone:    01203-523523 ext. 2541   (UK)  *
* CV4 7AL                                                                     * 
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