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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