Dear Josh,=

I have had this problem= many times before. This tells that your geometry does not correspond to th= e real local minimum. To check it you can submit a new optimization with yo= ur optimized geometry and consider opt=3Dreadfc guess=3Dread keywords (plea= se note that if you saved a chk file you can use these keywords!). If your = structure is the real minimum, the new job must finishes after just one cyc= le. However, I guess that, this is not the case for you.

<= span>To get the real minimum on the PES you may also consider opt=3D(calcal= l). Then, the second derivatives of energy will be computed in every step o= f optimization and you can be sure that you will find the real local minimu= m. Unfortunately, calcall keyword is very demanding because as I mentioned in every step of the optimization second derivatives of energy must be com= puted, this means that every optimization step is as demanding as a frequen= cy calculation.

Good luc= k

Cina Foroutan-Nejad

From: Jo= sh Marell mare0051-#-umn.edu <owner-chemistry#,#ccl.net>
To: "Foroutan-Nejad, Cina " &= lt;canyslopus#,#yahoo.co.uk>
Sent= : Monday, 14 November 2011, 1:33
Subject: CCL: Convergence During Frequency Analysis

Hello,

= I am optimizing a geometry at the m062x/6-31+g(d,p) level, and then I perfo= rm a frequency analysis. During the optimization step (and utilizing = opt=3Dverytight), I ensure that I am getting full convergence and see:=0A=0A=0A=0A

Maximum Force &n= bsp; 0.000000 0.000002 YES

RMS Force 0= .000000 0.000001 YES

Maximum Di= splacement 0.000005 0.000006 YES<= /div>

=0A=0A=0A=0A RMS Displacement 0.= 000001 0.000004 YES

<= div>However, then I carry out a frequency analysis using the following rout= e section:

# m062x/6-31+g(d,p) freq integral(ultrafinegrid) scrf= =3Dcheck geom=3Dcheckpoint

=0A=0A=0A=0A

And at the = end of the output file for the frequency analysis, it indicates in this spe= cific case that none of the criteria have converged (this is after the line= that specifies the axes has been restored to the original set)

=0A=0A=

Item &nbs= p; Value Threshold C= onverged?

=0A=0A

Maximum Force &= nbsp; 0.024599 0.000450 NO

RMS Force 0.= 005725 0.000300 NO

Maximu= m Displacement 0.311758 0.001800 = NO

RMS Displacement 0.083= 739 0.001200 NO

=0A=0A=0A=0A

&nb= sp;Predicted change in Energy=3D-4.741844D-03

GradGradGradG= radGradGradGradGradGradGradGradGradGradGradGradGradGradGrad

Is this telling me the results of the frequency analysis ar= e not reliable? I guess I'm unclear why the geometry that converged w= ith verytight requirement is now not converging during the frequency job (a= ssuming I'm understanding the implication of the above correctly).

=0A= =0A=0A

Thank you,

Josh

=0A=