From owner-chemistry@ccl.net Wed Nov 5 08:48:00 2008 From: "John McKelvey jmmckel-x-gmail.com" To: CCL Subject: CCL:G: convergence-maximum displacement Message-Id: <-38032-081105084524-26799-WHMdOwdiAMMuaDJQp+4Mzg.@.server.ccl.net> X-Original-From: "John McKelvey" Content-Type: multipart/alternative; boundary="----=_Part_10501_29155675.1225892709061" Date: Wed, 5 Nov 2008 08:45:09 -0500 MIME-Version: 1.0 Sent to CCL by: "John McKelvey" [jmmckel=gmail.com] ------=_Part_10501_29155675.1225892709061 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline There may be a very serious conceptual issue here. I am curious exactly what you are looking for. Are you just curious how to do a frequency calculation, or are you just interested in what the resulting lower energy vibrational modes and what the Max Disp might look like? With the Max Disp so large it is difficult to imagine the physical significance of doing a frequency calculation other wise. Cheers! John McKelvey On Tue, Nov 4, 2008 at 6:18 PM, Orlin Blajiev blajiev() vub.ac.be < owner-chemistry- -ccl.net> wrote: > > Sent to CCL by: Orlin Blajiev [blajiev^^vub.ac.be] > Hi again, > > I would like to post again the question about how to neglect the "Maximum > Displacement 0.125614 0.007200 NO" convergence option in > Gaussian. I would like just to proceed to a frequency calculation. > > Thanks very much in advance. > > Orlin > > > > >Sent to CCL by: "Kalju Kahn" [kalju+/-chem.ucsb.edu] > >Orlin, > > > >If you loosen these criteria too much, you will have a successful > >calculation but the structure found will be too far from the true minimum. > > Being able to do a calculation is not the same thing as being able to get > >the correct result. > > > >If you really want to neglect displacement conditions, just use the > >geometry that gave the results below (or pick a geometry with the lowest > >energy from your search). > > > >Your forces are small, the PES must be very flat in the region you are in: > >large changes in the structure will cause only small change in energy. > >You may want to make sure that your structure is a minimum, not a saddle > >point or a some plateau via frequency calculation. You should not have > >negative frequencies. After the frequency calculation, it will not hurt > >to try Opt=ReadFC, Geom=Check; you might find a better structure quickly > >using the correct Hessian. > > > >Kalju > > > >> > >> Sent to CCL by: Orlin Blajiev [blajiev%x%vub.ac.be] > >> Hi, > >> > >> I will appreciate an advise how to relax Maximum Displacement condition > >> (or neglect it althogether). I am already using IOP(1/7=1200). > >> > >> Maximum Force 0.000275 0.001800 YES > >> RMS Force 0.000063 0.001200 YES > >> Maximum Displacement 0.125614 0.007200 NO > >> RMS Displacement 0.017703 0.004800 NO > >> > >> Thank in advance. > >> > >> Orlin > >> > >> Orlin Blajiev > >> Electrochemical and Surface Engineering (SURF) > >> Faculty of Applied Science > >> Vrije Universiteit Brussel > >> Pleinlaan 2 - 1050 Brussels - Belgium > >> tel: ++32 2 6293538 - fax: ++32 2 6293200> > >> > >> > > > > > >~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > >Dr. Kalju Kahn > >Department of Chemistry and Biochemistry > >UC Santa Barbara, CA 93106> > > > > > > > > Orlin Blajiev > Electrochemical and Surface Engineering (SURF) > Faculty of Applied Science > Vrije Universiteit Brussel > Pleinlaan 2 - 1050 Brussels - Belgium > tel: ++32 2 6293538 - fax: ++32 2 6293200> > > ------=_Part_10501_29155675.1225892709061 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline There may be a very serious conceptual issue here.  I am curious exactly what you are looking for.  Are you just curious how to do a frequency calculation, or are you just interested in what the resulting lower energy vibrational  modes and what the Max Disp might look like? With the Max Disp so large it is difficult to imagine the physical significance of doing a frequency calculation other wise.

Cheers!

John McKelvey

On Tue, Nov 4, 2008 at 6:18 PM, Orlin Blajiev blajiev() vub.ac.be <owner-chemistry- -ccl.net> wrote:

Sent to CCL by: Orlin Blajiev [blajiev^^vub.ac.be]
Hi again,

I would like to post again the question about how to neglect the "Maximum Displacement     0.125614     0.007200     NO" convergence option in Gaussian. I would like just to proceed to a frequency calculation.

Thanks very much in advance.

Orlin

>
>Sent to CCL by: "Kalju Kahn" [kalju+/-chem.ucsb.edu]
>Orlin,
>
>If you loosen these criteria too much, you will have a successful
>calculation but the structure found will be too far from the true minimum.
> Being able to do a calculation is not the same thing as being able to get
>the correct result.
>
>If you really want to neglect displacement conditions, just use the
>geometry that gave the results below (or pick a geometry with the lowest
>energy from your search).
>
>Your forces are small, the PES must be very flat in the region you are in:
>large changes in the structure will cause only small change in energy.
>You may want to make sure that your structure is a minimum, not a saddle
>point or a some plateau via frequency calculation.  You should not have
>negative frequencies.   After the frequency calculation, it will not hurt
>to try Opt=ReadFC, Geom=Check; you might find a better structure quickly
>using the correct Hessian.
>
>Kalju
>
>>
>> Sent to CCL by: Orlin Blajiev [blajiev%x%vub.ac.be]
>> Hi,
>>
>> I will appreciate an advise how to relax  Maximum Displacement condition
>> (or neglect it althogether). I am already using IOP(1/7=1200).
>>
>> Maximum Force            0.000275     0.001800     YES
>>  RMS     Force            0.000063     0.001200     YES
>>  Maximum Displacement     0.125614     0.007200     NO
>>  RMS     Displacement     0.017703     0.004800     NO
>>
>> Thank in advance.
>>
>> Orlin
>>
>> Orlin Blajiev
>> Electrochemical and Surface Engineering (SURF)
>> Faculty of Applied Science
>> Vrije Universiteit Brussel
>> Pleinlaan 2 - 1050 Brussels - Belgium
>> tel: ++32 2 6293538 - fax: ++32 2 6293200>
>>
>>
>
>
>~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>Dr. Kalju Kahn
>Department of Chemistry and Biochemistry
>UC Santa Barbara, CA 93106>
>
>
>

Orlin Blajiev
Electrochemical and Surface Engineering (SURF)
Faculty of Applied Science
Vrije Universiteit Brussel
Pleinlaan 2 - 1050 Brussels - Belgium
tel: ++32 2 6293538 - fax: ++32 2 6293200



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