UT theoretical chemistry code forum

Thank you.Sorry,I just misread the numbers.I appreciate your kind help.

Thank you...I have some doubts

How I can calculate ZPE/Svib in presence of imaginary frequencies to reproduce calculations as attached? dymmatrix.pl will ignore them?

In the case of of surface_adsorbate and clean surface calculations I managed to get all real frequency but never get same with ...

Dear Dr.Graeme

I am trying to use dynamic matrix to get vibratioonal frequencies for some simple molecules in box.
I started with methane relaxation at PREC= High ,then followed by dynamic matrix calculations (files attached).However,the imaginary frequencies persist even after increasing the ...

Thank you for the explanation.
In fact, I am working with temperature 800-1000K (that is considered in high Temperature,is n't it?) so I used that simple classical form k(T)=A exp (-Ea/KbT) where A is from dymprefactor.pl/Vineyard and I plug in the Ea directly from NEB results for few calculation ...

Dear Dr.Graeme,

Currently I am calculating the rate constant for elementary reactions.I am using the simple harmonic TS theory and calculating the prefactor using dymprefactor.pl

for that I use the simple form k(T)=A exp (-Ea/KbT) where A is prefactor form the script and Ea is the energy barrier ...

Dear Dr.Graeme ,

Crystal clear! ..Thank you very much for your help.

Regards,
A.Omran

Dear Dr.Graeme,

I have continued with neb calculation more close to 0.01 eV Force as follow
0 0.007584 -183.098500 0.000000
1 0.006079 -182.749800 0.348700
2 0.003504 -182.516000 0.582500
3 0.001 476 -182.209900 0.888600
4 0.017795 -182.319100 0.779400
5 0.027094 -182.352200 0.746300
6 ...

Dear Dr.Graeme,
Thank you for advice.
-Totally agree with your suggestion,I set up NEB calculation to continue further to less than -0.05 eV using FIRE.

-Thanks for the tip about stopping reaction if Dimer cross from -ve to +ve curvature .In fact, I have just faced this problem with CH4 ...

Thanks for your reply.
Here is the calculation details
First ,I have started with 6 images using QM and get
0 0.007584 -183.098500 0.000000
1 0.014441 -182.642100 0.456400
2 0.018104 -182.490600 0.607900
3 0.078443 -182.197500 0.901000
4 0.098946 -182.266200 0.832300
5 0.088267 -182 ...

Dear Dr.Graeme,
For the reaction of H+H-->H2 over Ni-based catalyst,I have successfully performed cNEB followed by Dimer to get the T.S. with calculation converged to the given setting of -0.01eV. Trying to use dynamic matrix to find imaginary frequecy/ZPE ,multiple imaginarg frequencies are ...

Hi Andrew,

Thank you very much for your insights and detail.I have already tried dimmin.pl with the 0.1 displacement and with now change in the result still same with "negative" barrier .I will give another chance with 0.2/0.3 displacements to see if any difference.

Meanwhile,I will try a new ...

Dear Prof.Graeme,
Extending my gratitude for your kind support,I have gone for both ways to confirm the reaction mechanism.

Initially,I confirmed that I got the right saddle point by dynamic matrix which resulted in only 1 imaginary vibrations @848.34 cm-1 .Then from that T.S.:

(a)Dimer:Using ...

Dear Prof.Dr.Graeme,

Thank you very much for your suggestion,

(a)I have put your latest suggestion about intermediate convergence into action and waiting the results..just to clarify (please correct me if I am wrong):
1-I will minimize image 04 and consider it as my final state instead of my ...

Dear Prof.Graeme,

After reach below 0.1 force ,I switched to IOPT=1(LBFGS) as discussed ,After 450 steps the forces seems are not going down or very very slow (attached) .Should I consider FIRE or try DIMER better?

Thanks for your help
Omran

Please find attached calculations