From owner-chemistry@ccl.net Fri Sep 23 02:59:00 2011 From: "ABHISHEK SHAHI shahi.abhishek1984#gmail.com" To: CCL Subject: CCL:G: G09: Convergence Issues for H-Bonded Systems Message-Id: <-45500-110923024857-27034-QTFxv2D0Qumo+vtFwUoKQQ{}server.ccl.net> X-Original-From: ABHISHEK SHAHI Content-Type: multipart/alternative; boundary=0016e6506128898f9604ad9633c0 Date: Fri, 23 Sep 2011 12:18:28 +0530 MIME-Version: 1.0 Sent to CCL by: ABHISHEK SHAHI [shahi.abhishek1984*_*gmail.com] --0016e6506128898f9604ad9633c0 Content-Type: text/plain; charset=ISO-8859-1 Dear Sam , Once i solved the problem of negative frequencies by *subtracting or adding * the coordinates of negative frequency (Get it from freq. calculation)* to the* molecular specification coordinates (it should be the final coordinates in which negative frequency exist). If its painful then use matlab or any matrix adding/subtracting program to make the addition or subtraction easy. Hope it may work for you. By doing this we are mainly working against the negative frequency. hopefully you are using the keyword "nosymm" along with all others. Thanks & regards; *ABHISHEK SHAHI* *Research Scholar Inorganic and Physical Chemistry Indian Institute Of Science Bangalore-12* India E-mail: shahi#%#ipc.iisc.ernet.in shahi.abhishek1984#%#gmail.com On Thu, Sep 22, 2011 at 10:59 PM, Arne Dieckmann adieckma^googlemail.com < owner-chemistry#%#ccl.net> wrote: > > Sent to CCL by: Arne Dieckmann [adieckma . googlemail.com] > I would not consider -1.9 wavenumbers an imaginary frequency. Have a look > at the Gaussian manual and whitepapers, there is a section about this issue. > > Cheers, > Arne > > On Sep 22, 2011, at 8:25 AM, Sam Abrash sabrash]_[richmond.edu wrote: > > > > > 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! > > Sam> > > --0016e6506128898f9604ad9633c0 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Dear Sam ,

=A0Once i solved the problem of negative frequencies by = subtracting or adding the coordinates of negative frequency (Get it = > from freq. calculation) to the molecular specification coordinates (= it should be the final coordinates in which negative frequency exist). If i= ts painful then use matlab or any matrix adding/subtracting program to make= the addition or subtraction easy. Hope it may work for you. By doing this = we are mainly working against the negative frequency. hopefully you are usi= ng the keyword "nosymm" along with all others.=A0




Thanks & = regards;
=A0<= font style=3D"font-family:trebuchet ms,sans-serif" size=3D"4">ABHISHEK SHAHI

Research ScholarInorganic= and Physical Chemistry
In= dian Institute Of Science
Bangalore-12
India
E-mail: =A0=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 shahi#%#ipc.iisc.ernet.in
=A0 =A0 =A0 =A0 =A0 =A0 = =A0 =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 shahi.abhishek1984#%#gmail.com




On Thu, Sep 22, 2011 at 10:59 PM, Arne D= ieckmann adieckma^googlemail.com <owner-chemistr= y#%#ccl.net> wrote:

Sent to CCL by: Arne Dieckmann [adieckma . googlemail.com]
I would not consider -1.9 wavenumbers an imaginary frequency. Have a look a= t the Gaussian manual and whitepapers, there is a section about this issue.=

Cheers,
Arne

On Sep 22, 2011, at 8:25 AM, Sam Abrash sabrash]_[richmond.edu wrote:

>
> 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= cation. =A0I'm having trouble with the geometric convergence. =A0I was= able to get the system to converge with normal convergence criteria, opt= =3Dcalcall, and MaxStep=3D5, but then I got an imaginary frequency of -1.9 = wavenumbers.
>
> 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 displa= cement criteria. =A0Both this observation and looking at the structures wit= h JMOL show that the problem is finding the minimum in a very shallow poten= tial.
>
> Two questions. =A0First, is the 1.9 wavenumber imaginary frequency rea= l or an artifact? =A0Second, any advice on how to force the system to conve= rge? =A0Model chemistry is M062X/6-311++G**.
>
> Thanks!
> Sam>
>



-=3D This is automatically added to each message by the mailing script =3D-=
E-mail to subscribers: CHEMISTRY#%#ccl.n= et or use:
=A0 =A0 =A0http://www.ccl.net/cgi-bin/ccl/send_ccl_message

E-mail to administrators: CHEM= ISTRY-REQUEST#%#ccl.net or use
=A0 =A0 =A0http://www.ccl.net/cgi-bin/ccl/send_ccl_message

Subscribe/Unsubscribe:
=A0 =A0 =A0http://www.ccl.net/chemistry/sub_unsub.shtml

Before posting, check wait time at: http://www.ccl.net

Job: http://www.ccl.n= et/jobs
Conferences: http://server.ccl.net/chemistry/announcements/co= nferences/

Search Messages: http://www.ccl.net/chemistry/searchccl/index.shtml
=A0 =A0 =A0h= ttp://www.ccl.net/spammers.txt

RTFI: http://www.ccl.net/chemistry/aboutccl/instructions/



--0016e6506128898f9604ad9633c0--