Dear S. Xavier

It is not easy to write equations and paste schemas in this message. So, if not allready donne, please don't hésitate to go to the following reference:

Bredas, J. L.; Beljonne, D.; Coropceanu, V.; Cornil, J., Charge-transfer and energy-transfer processes in pi-conjugated oligomers and polymers: A molecular picture. Chemical Reviews 2004, 104 (11), 4971-5003.

I have attached a paper of mine also (see the section computational details).

Please let me know if these don't seem clear to you.

Regards,

Gjergji Sini

Dear Gjergji Sini

Thank you so much for your help

I shall try

Fr.Xavier

Dear Gjergji Sini

I downloaded the paper, but I was not able to find out the key words to calculate  for

λ= λ1+λ2 in Gaussian 09w software

Please do help me

Fr.Xavier

Dear Fr.Xavier

There are no keywords for lambda calculations in gaussian. 

All you need is

1- optimise the geometry of the neutral molecule (GS)

2- calculate cation energy with the GS geometry

3- optimize the geometry of the cation

4- calculate the neutral molecule with the geometry of the cation

Then,

lambda1=E(4) -E(1)

lambda2=E(2) -E(3)

That's all.

Please let me know if anything is not clear

Regards

Gjergji

Dear Gjergji

Thank you so much

I shall try

Fr.Xavier

Dear Prof. Gjergji Sini,

How to obtain cation energy with the GS geometry ? do you have the example input file in gaussian? I was also looking for the reorganization energy. Thank you very much for the helps

Best, Salmahaminati

Dear Salmahaminati,

I am extremely sorry for seeing your question so late.

In case you still need this answer:

once the GS geometry has finished being optimized, just pick up the final geometry (for example from the checkpoint file "geom=check"), and perform a single point calculation by putting "1 2" for the charge- and spin multiplicity of the cation species, as compared to "0 1" for the neutral molecule.

Again, all my apologies for this late response.

Best regards

Gjergji

Dear Prof. Gjergji Sini

I already got the answer from your reply in email. Thank you so much!

Dear Saravanan Chinnusamy

Thank you very much for the information :)

Best Regards, Salmahaminati

Dear Sir, Gjergji Sini , I have gone through your publication with doi: dx.doi.org/10.1021/jp2098872, I have a question regarding the electronic coupling (t) and ΔG°. Can you please explain how to calculate the electronic coupling (t) and ΔG° using Gaussian ?

Dear Ranjan,

Please find below some indiations how to calculate DG° and the transfer integrals by means of Gaussian (09).

A- DG°

This is the easiest:

- if you are calculating a dimer, then DG° =0 (as a first approxiation) as the molecules are identical

- If you are calculating a complex (for instance a D-A complex), then DG° = E(CT), which is the energy of the lowest Charge transfer excited state. This last one can be calculated for instance at the TDDFT level.

B- transfer integrals (t) between molecular orbitals (different from t between states)

Actually, Gaussian doesn't calculate the transfer integrals by itself. Instead, you can use it to calculate the Overlap and Fock matrix.

After that, you can write a quick code to use them in a formula giving you the transfer integrals between MOs (the easiest way is to use the formula given for instance in Valeev et al., J. Am. Chem. Soc. , 2006, 128 (30), pp 9882–9886 ) In order to obtain the necessary matrices to be used in the formula of the cited paper, you need  to perform three independent calculations:

1- Optimize the dimer geometry (or D-A complex) in the neutral state. This is not mandatory if you use geometries deduced from dynamic simulations. If this is the case, then you can skip this step.

2- Perform SP calculations for each fragment isolated from the geometry of the dimer (complex). This will provide the MO matrix of each fragment.  The Gaussian09 keyword line must contain at least the following standard and particular keywords:

# B3LYP/6-31G(d,p) guess=.......  nosymm punch(mo)

# scf=(direct,nosymm)

B3LYP/6-31G(d,p) is here an example but you can use any level you need.

Please note that the keywords in bold are mandatory !!

3- Perform one Gaussian09 Single Point calculation on the dimer (or complex), which will provide two matrices: the fock and the overlap ones in the basis of the atomic orbitals. The keyword line must contain at least the following standard and particular keywords:

# B3LYP/6-31G(d,p) guess=......  nosymm pop=nboread

# scf=(direct,nosymm)

After the geometry section you must add the following:

......................................................................

 H                 -8.23907700   -4.48731100   -0.08878300 (coordinates of the last atom)

empty line

$NBO SAO=w53 FAO=W54 $END

empty line

Here, "SAO=w53 FAO=W54" indicates the Overlap and Fock matrices between atomic orbitals. The numbers 53 and 54 are freely defined by the user, and can be whatever (except probably "10", which mayby is used by the NBO program, and less than 1000). 

I hope this helps.

Enjoy!

Best regards,

Gjergji

Gjergji Sini Thanks for your reply.

Gjergji Sini I have found your answer very helpful. One question is - the number of basis functions will be different for the fragment and the full system. So the size of the required matrices will be also different. So, what should be done? because we need the size of the matrices to match to do multiplication.

For the calculation of lambda do I have calculate using solvent or should I do it in gas phase? Is there a detailed procedure available for the calculation of the reorganization energy?

Gjergji Sini sir, thanks for replying... i will also calculate reorganization energy.. but on Linux, is there any input file for calculating?

Dear S. Xavier

For more clarity, I have attached the input files necessary for the calculations of the energies you need. For the example case, I applied this procedure on the water molecule (H2O). If there are any problems please let me know.

Best Regar, Ousmanou marius

Thank you sir. S. Xavier for posting this question and thank you sir. Gjergji Sini and Marius Ousmanou for all the use full information! I have tried to follow the calculation with the ion pairs of SF6+ and SF6-, however I ended up with getting negative reorganization energy, is it normal or could you give me some suggestions? I would like to calculate electron transfer rate with this calculation but I think this negative reorganization energy will give me something like sqrt(negative) issue. (I did not add scrf keyword since I want to keep it gas phase). Thank you very much.

Dear Zhibo Liu I have already encountered this in my calculations and I do not have any useful references which can explain this result. However, it is necessary that the two energies have the same sign and the negative sign simply denotes the direction of the reaction, which, in reality, occurs in the opposite direction to the direction previously chosen.

Another way to observe these results is to try another DFT functional or another basis set because the reorganization energies are very sensitive to the method.

Best regard.

Thank you Sir. Marius Ousmanou . I will try to use some order basis to see if the results agree with each other! In addition, have you ever tried to obtain the reorganization energy of monoatomic species? I am not sure if it is even meaningful to think about it.