From owner-chemistry@ccl.net Wed Mar 18 10:35:01 2015 From: "Mark Zottola mzottola*o*gmail.com" To: CCL Subject: CCL:G: Gaussian Job Message-Id: <-51138-150318103302-7791-QxTy9zUxWtebc9MxKc3/wA.@.server.ccl.net> X-Original-From: Mark Zottola Content-Type: multipart/alternative; boundary=e89a8ffbae418b2802051190f5e7 Date: Wed, 18 Mar 2015 21:32:55 +0700 MIME-Version: 1.0 Sent to CCL by: Mark Zottola [mzottola^^^gmail.com] --e89a8ffbae418b2802051190f5e7 Content-Type: text/plain; charset=UTF-8 Gaussian has one of the best optimizers for QM. Before trashing G09, make sure your structure is indeed correct chemically. Second, optimizing a structure at a lower level of theory and then re-optimizing at a higher level of theory often (not always) overcomes convergence issues wrt structure. Thirdly, your comments are ambiguous. Do you mean to say that the wavefunction did not converge or that there were difficulties in getting a converged wavefunction? Or do you mean the optimization did not converge? If the latter and there is not an issue with cpu time, why quit on Gaussian? If your issue is with the convergence of the wavefunction alone, then there is plenty on both the G09 web site and the CCL archives about approaches to dealing with unstable wavefunctions. If your system is pathogenic using G09 and wish to explore another program NWCHEM, a very-well parallelized QM code might be better than GAMESS. THe former is also free, assuming you have no export considerations to contend with. On Wed, Mar 18, 2015 at 6:51 PM, Sergio Manzetti sergio.manzetti*outlook.com wrote: > > Sent to CCL by: "Sergio Manzetti" [sergio.manzetti__outlook.com] > Thanks Brian. At the end of the day, G09 was not able to solve this > structure. I am trying GAMESS instead, however I cannot find an equivalent > to CASSCF method in the example section of GAMESS US. Can anyone recommend > the most accurate method to treat a very small system (Computational time > and speed is irrelevant)? > > Thanks> > > --e89a8ffbae418b2802051190f5e7 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
Gaussian has one of the best optimizers for QM.=C2=A0 Befo= re trashing G09, make sure your structure is indeed correct chemically.
Second, optimizing a structure at a lower level of theory a= nd then re-optimizing at a higher level of theory often (not always) overco= mes convergence issues wrt structure.

Thirdly, you= r comments are ambiguous.=C2=A0 Do you mean to say that the wavefunction di= d not converge or that there were difficulties in getting a converged wavef= unction?=C2=A0 Or do you mean the optimization did not converge?=C2=A0 If t= he latter and there is not an issue with cpu time, why quit on Gaussian?

If your issue is with the convergence of the wavefun= ction alone, then there is plenty on both the G09 web site and the CCL arch= ives about approaches to dealing with unstable wavefunctions.
If your system is pathogenic using G09 and wish to explore anot= her program NWCHEM, a very-well parallelized QM code might be better than G= AMESS.=C2=A0 THe former is also free, assuming you have no export considera= tions to contend with.

On Wed, Mar 18, 2015 at 6:51 PM, Sergio Manzetti sergio.ma= nzetti*outlook.com <= ;owner-chemist= ry###ccl.net> wrote:

Sent to CCL by: "Sergio=C2=A0 Manzetti" [sergio.manzetti__outlook.com]=
Thanks Brian. At the end of the day, G09 was not able to solve this structu= re. I am trying GAMESS instead, however I cannot find an equivalent to CASS= CF=C2=A0 method in the example section of GAMESS US. Can anyone recommend t= he most accurate method to treat a very small system (Computational time an= d speed is irrelevant)?

Thanks



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