From owner-chemistry@ccl.net Thu Sep 22 19:31:01 2011 From: "Bradley Welch bwelch5^^^slu.edu" To: CCL Subject: CCL:G: G09: Convergence Issues for H-Bonded Systems Message-Id: <-45499-110922193004-32757-2hQZ+RF71l3bthYGcDRFJA a server.ccl.net> X-Original-From: Bradley Welch Content-Type: multipart/alternative; boundary=0015176f0a88b22a5c04ad90111b Date: Thu, 22 Sep 2011 18:29:50 -0500 MIME-Version: 1.0 Sent to CCL by: Bradley Welch [bwelch5 a slu.edu] --0015176f0a88b22a5c04ad90111b Content-Type: text/plain; charset=ISO-8859-1 Have you optimized the system at a lower level of theory and have had success? Bradley Welch On Thu, Sep 22, 2011 at 5:08 PM, Sten Nilsson Lill stenil-x-chalmers.se < owner-chemistry*ccl.net> wrote: > > Sent to CCL by: Sten Nilsson Lill [stenil||chalmers.se] > Sam, > > in similar cases I've been able to reach convergence by using the keywords > scf=novaracc and opt=(tight,newton). To those opt-keyword you could also add > calcfc as you mention. > > Another aspect of this is the sensitivity of the M06 functionals to the > choice of integration grid. It's recommended to use a large grid so if you > are using Gaussian you can try Grid=ultrafine. Remember that it will be more > costly and that you need to do all your calculations with the same grid > settings when comparing energies. > > You can read more on this in Houk's JCTC paper from 2010: > http://pubs.acs.org/doi/abs/10.1021/ct900639j and some references therein, > for example some work by DiLabio and Johnson. > > Hope that helps, > > Sten > > Ph.D. Sten Nilsson Lill > Dep. of Chemistry > University of Gothenburg > SE-412 96 Gothenburg, Sweden > e-mail: stenil^-^chem.gu.se > Phone: +46-31 786 9103 > Fax: +46-31-772 3840 > ________________________________________ > > From: owner-chemistry+stenil==chem.gu.se^-^ccl.net[owner-chemistry+stenil== > chem.gu.se^-^ccl.net] On Behalf Of Sam Abrash sabrash]_[richmond.edu[owner-chemistry^-^ > ccl.net] > Sent: Thursday, September 22, 2011 5:25 PM > To: Nilsson Lill, Sten > Subject: CCL: G09: Convergence Issues for H-Bonded Systems > > Sent to CCL by: "Sam Abrash" [sabrash_+_richmond.edu] > Hi Folks, > > I have a job involving hydrogen bonding of 3 acetylenes to the benzene > cation. I'm having trouble with the geometric convergence. I was able to > get the system to converge with normal convergence criteria, opt=calcall, > and MaxStep=5, but then I got an imaginary frequency of -1.9 wavenumbers. > > Subsequently, I changed to Opt=tight, tried both calcfc and calcall, and > have steadily reduced MaxStep to 1, but it still won't converge. The force > constant criteria have been met, but the problem is the displacement > criteria. Both this observation and looking at the structures with JMOL > show that the problem is finding the minimum in a very shallow potential. > > Two questions. First, is the 1.9 wavenumber imaginary frequency real or an > artifact? Second, any advice on how to force the system to converge? Model > chemistry is M062X/6-311++G**. > > Thanks! > Samhttp:// > www.ccl.net/cgi-bin/ccl/send_ccl_messagehttp://www.ccl.net/chemistry/sub_unsub.shtmlhttp://www.ccl.net/spammers.txt> > > --0015176f0a88b22a5c04ad90111b Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Have you optimized the system at a lower level of theory and have had succe= ss?


Bradley Welch


On Thu,= Sep 22, 2011 at 5:08 PM, Sten Nilsson Lill stenil-x-chalmers.se <owner-chemistry*ccl.net> wrote:

Sent to CCL by: Sten Nilsson Lill [stenil||chalmers.se]
Sam,

in similar cases I've been able to reach convergence by using the keywo= rds scf=3Dnovaracc and opt=3D(tight,newton). To those opt-keyword you could= also add calcfc as you mention.

Another aspect of this is the sensitivity of the M06 functionals to the cho= ice of integration grid. It's recommended to use a large grid so if you= are using Gaussian you can try Grid=3Dultrafine. Remember that it will be = more costly and that you need to do all your calculations with the same gri= d settings when comparing energies.

You can read more on this in Houk's JCTC paper from 2010: http://pubs.= acs.org/doi/abs/10.1021/ct900639j and some references therein, for exam= ple some work by DiLabio and Johnson.

Hope that helps,

Sten

Ph.D. Sten Nilsson Lill
Dep. of Chemistry
University of Gothenburg
SE-412 96 Gothenburg, Sweden
e-mail: stenil^-^chem.gu.se=
Phone: +46-31 = 786 9103
Fax: +46-31-772 = 3840
________________________________________
> From: owner-chemistry+stenil=3D=3Dchem.gu.se^-^c= cl.net [owner-chemistry+stenil=3D=3Dchem.gu.se^-^= ccl.net] On Behalf Of Sam Abrash sabrash]_[richmond.edu [owner-chemistry^-^ccl.net]
Sent: Thursday, September 22, 2011 5:25 PM
To: Nilsson Lill, Sten
Subject: CCL: G09: Convergence Issues for H-Bonded Systems

Sent to CCL by: "Sam =A0 Abrash" [sabrash_+_richmond.edu]
Hi Folks,

I have a job involving hydrogen bonding of 3 acetylenes to the benzene cati= on. =A0I'm having trouble with the geometric convergence. =A0I was able= to get the system to converge with normal convergence criteria, opt=3Dcalc= all, and MaxStep=3D5, but then I got an imaginary frequency of -1.9 wavenum= bers.

Subsequently, I changed to Opt=3Dtight, tried both calcfc and calcall, and = have steadily reduced MaxStep to 1, but it still won't converge. =A0The= force constant criteria have been met, but the problem is the displacement= criteria. =A0Both this observation and looking at the structures with JMOL= show that the problem is finding the minimum in a very shallow potential.<= br>
Two questions. =A0First, is the 1.9 wavenumber imaginary frequency real or = an artifact? =A0Second, any advice on how to force the system to converge? = =A0Model chemistry is M062X/6-311++G**.

Thanks!
Samhttp://www.ccl.net/cgi-bin/ccl/send_ccl_messagehttp://www.ccl.n= et/chemistry/sub_unsub.shtmlhttp://www.ccl.net/spammers.txt


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