[molpro-user] Problem regarding IRC with method QSDPATH
G Mahesh
gmahesh at students.iiserpune.ac.in
Tue Aug 27 18:02:16 BST 2013
Dear Ramon,
Thanks for the suggestions, Now the problem is almost solved. First I have
done transition state optimization by using central differences method to
calculate Hessian as you suggested and got transition state with one
imaginary frequency and I also have started IRC with this transition state
geometry. Now, though it's still running but, it's doing well which means
it has done 6 steps yet. So, with this I don't have any problems.
Now, I have small doubt which I'll explain below as much clear as I can.
First, by using the above mentioned procedure I got transition state, here
is the partial output which is showing that the energy is converged.
Numerical MULTI000 hessian completed. CPU-time: 14959.95 sec, Elapsed:
15756.64 sec
MULTI hessian saved to record 5300.2
4 -353.92204742 -353.92205201 -0.00000458 0.00262178 0.00270543
0.00030060 0.01644770 0.02796584 0.01250670 30537.85
5 -353.92205201 *-353.92205134* 0.00000067 0.00016687
0.00021778 0.00002420 0.02154643 0.02706698 0.01210472 31486.08
END OF GEOMETRY OPTIMIZATION.
Now I have started IRC with the coordinates of TS which I got from above
output. Here (IRC input), first it'll do transition state optimization and
after that it'll start IRC. Since I am doing transition state optimization
with transition state geometry it supposed to be done within single step.
But, it hasn't, it took 4 steps again to converge. Let me post the part of
IRC output too.
1 *-353.92205134* -353.92205323 -0.00000190 0.00048402
0.00056518 0.00006280 0.05066241 0.05339754 0.02388011 13641.47
2 -353.92205323 -353.92205329 -0.00000005 0.00067958 0.00073450
0.00008161 0.01391002 0.01394040 0.00623434 14417.26
3 -353.92205329 -353.92205336 -0.00000008 0.00032270 0.00033121
0.00003680 0.00648028 0.00668994 0.00299183 15217.03
Numerical MULTI000 hessian completed. CPU-time: 13239.33 sec, Elapsed:
13652.13 sec
MULTI hessian saved to record 5300.2
4 -353.92205336 -353.92205342 -0.00000006 0.00014249 0.00015385
0.00001709 0.01205479 0.01211916 0.00541985 28400.79
END OF GEOMETRY OPTIMIZATION.
Is this usual......? How could we explain this ....?
On Fri, Aug 23, 2013 at 10:17 PM, Ramon Hernandez <ramon at uaem.mx> wrote:
> Dear Mahi,
>
> I see two problems with your calculations:
>
> a) The estimate of frequencies with central differences should be more
> reliable and
> this calculation shows four negative hessian eigenvalues so doing an
> IRC at this
> geometry is not correct. Look at the manual page for frequency
> calculations.
>
> b) The program is complaining about the gradient value it seems it is not
> small
> enough to be considered converged for a stationary point.
>
> I think first you have to make sure that you have really found a
> transition state
> with only one imaginary frequency doing the calculation with central
> differences.
>
> Cheers
>
> Ramon
>
> 2013/8/23, G Mahesh <gmahesh at students.iiserpune.ac.in>:
> > Dear Ramon,
> >
> > I thought, the problem arising in IRC was because of negative Hessian
> > eigenvalues but, now I realized that's not the case. Earlier I have done
> > transition state optimization with Hessian calculated by forward
> > differences and IRC with central differences so that, it was giving 4
> > negative Hessian values in the case of IRC.
> >
> > Now I ran IRC with calculating Hessian using forward differences and all
> > positive Hessian eigenvalues except one got too. Even now also
> surprisingly
> > giving the same error which I got earlier. Here, I also have posted the
> > echo of output having error.
> >
> > ***********Partial out put************
> >
> > Geometry optimization using default procedure for command MULTI
> >
> > Geometry written to block 1 of record 700
> >
> > Generated 9 symmetrical displacements
> >
> > Numerically approximating hessian using forward gradient differences
> >
> > Task list generated. Total number of displacements: 9
> >
> > 5 tasks completed, CPU=1h 3m 15s Elapsed=1h 10m 13s
> >
> > Numerical MULTI000 hessian completed. CPU-time: 6877.21 sec, Elapsed:
> > 7645.49 sec
> >
> > MULTI hessian saved to record 5300.2
> >
> > Quadratic Steepest Descent - Reaction Path Following using exact
> Hessian
> >
> > Hessian eigenvalues: -0.012734 0.000786 0.011948 0.018747
> 0.075415
> > 0.141616 0.303108 1.646533 1.810536
> >
> > IDIR= 1 requested but starting point is not a stationary point. Gradient
> > norm= 0.98D-04 Step length= 0.36D-01
> > ? Error
> > ? Not a stationary point
> > ? The problem occurs in QSDPATH1
> > ***********
> >
> > What's wrong I am doing here....??
> >
> > Thanks,
> >
> > Mahi.
> >
> >
> >
> > On Wed, Aug 21, 2013 at 9:18 PM, Ramon Hernandez <ramon at uaem.mx> wrote:
> >
> >> Dear Mahi,
> >>
> >> I suggest you double-check that indeed your initial CASSCF calculation
> >> corresponds
> >> to a transition state, perhaps run a frequency calculation with tight
> >> parameters. Then
> >> when you run the IRC make sure you indeed converge to the same energy
> >> as the original
> >> CASSCF calculation. If you are sure about both these points then the
> >> problem might really
> >> have to do with a bug in IRC.
> >>
> >> Also if you run again the initial frequency calculation you can save
> >> that information and
> >> then read it directly in the next IRC job so you avoid calculating it
> >> twice.
> >>
> >> Cheers
> >>
> >> Ramon
> >>
> >> 2013/8/21, G Mahesh <gmahesh at students.iiserpune.ac.in>:
> >> > Dear all,
> >> >
> >> > I am familiar with MOLPRO from last two months. Since then I am trying
> >> > to
> >> > find a transition state for the reaction of reactants and products
> >> > having
> >> > multi reference character so, I am using CASSCF method for my problem.
> >> > After a long struggle, I have found the transition state with one
> >> imaginary
> >> > frequency (150 cm-1) and this normal mode having imaginary frequency
> >> seems
> >> > like reaction mode which will connect reactants to products.
> >> >
> >> > Now the problem is with IRC, here, I started IRC with the geometry
> >> > which
> >> I
> >> > got from the transition state optimization with QSDPATH method and
> >> > IDIR=1
> >> > then, after Hessian calculation, it's complaining that, the given
> >> structure
> >> > is not stationary with 4 negative Hessian eigenvalues. Does this
> means,
> >> my
> >> > initial structure is not real transition state structure.....??
> Should
> >> > I
> >> > have to try for the transition state structure again ..?? Any ideas to
> >> > solve the problem....?? Pls help me...!
> >> >
> >> > Below additional details may be required to understand the problem.
> >> >
> >> > We are using the MOLPRO version 2012.
> >> > Our system has 5 atoms. We are using 13 active orbitals and 15 active
> >> > electrons as my cas space and AVTZ as basis.
> >> >
> >> > Thanks,
> >> > Mahi
> >> >
> >>
> >
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.molpro.net/pipermail/molpro-user/attachments/20130827/432d294a/attachment.html>
More information about the Molpro-user
mailing list