Mr. Saisudhakar,

Gaussian has not option to compute dielectric constant from refractive index.

It can compute given set of tensor components of different order (hyper)polarizabiliy tensor components, including at different solution using different models, PCM, for example, and than the refractive index can be calculated using many available expressions, depending of the system studied, where are included the ith order susceptibilities, respectively. Please pay attention to Eqs in the attachment as well as to the discussion connected with the computing of different order polarizabilities by Gaussian:

How can I get hyperpolarizability in Gaussian 09 output? (http://www.researchgate.net/post/How_can_I_get_hyperpolarizability_in_Gaussian_09_output).

For solution, meaning a system that you would like to compute the refractive index has expression similar the Eq.(4) where is included the real part of X(3), i.e. ReX(3).

So that you should write a program module using the relationship in [ref. 1], for example, joining the solution of the non-equilibrium solvation problem to PCM, where are given the relationships between the static and the fast dielectric constant of given medium with the corresponding order susceptibilities, in addition to a module connecting refractive index with the susceptibility. In this way you shall join the refractive index (the measured value I suppose) with the dielectic constants.

[ref. 1]  R. Cammi, J. Tomasi, International Journal of Quantum Chemistry, 29, 465 -474 (1 995).

Mr. Saisudhakar,

Gaussian has not option to compute dielectric constant from refractive index.

It can compute given set of tensor components of different order (hyper)polarizabiliy tensor components, including at different solution using different models, PCM, for example, and than the refractive index can be calculated using many available expressions, depending of the system studied, where are included the ith order susceptibilities, respectively. Please pay attention to Eqs in the attachment as well as to the discussion connected with the computing of different order polarizabilities by Gaussian:

How can I get hyperpolarizability in Gaussian 09 output? (http://www.researchgate.net/post/How_can_I_get_hyperpolarizability_in_Gaussian_09_output).

For solution, meaning a system that you would like to compute the refractive index has expression similar the Eq.(4) where is included the real part of X(3), i.e. ReX(3).

So that you should write a program module using the relationship in [ref. 1], for example, joining the solution of the non-equilibrium solvation problem to PCM, where are given the relationships between the static and the fast dielectric constant of given medium with the corresponding order susceptibilities, in addition to a module connecting refractive index with the susceptibility. In this way you shall join the refractive index (the measured value I suppose) with the dielectic constants.

[ref. 1]  R. Cammi, J. Tomasi, International Journal of Quantum Chemistry, 29, 465 -474 (1 995).

Dear Bojidarka,

I am a beginner with G09. My project is concerned with UV-Vis absorbance and fluorescence. Could you please advise where i can find templates for route sections for determination of 1) Absorption spectrum 2) Fluorescence spectrum 3) kind of transition e.g. S0---S1 4) Charge transfer 5) n-pi* or pi-pi* transitions 6) Stoke's shift and transition energy 7) .........

Dear Muhammad,

U can use this Gaussian link ( http://www.gaussian.com/g_tech/g_ur/k_scrf.htm )  for absorption and emission procedure in presence of solvent and gas phase with example..

Thanks, but i already reviewed gaussian website that u sent. i need a tutorial for every job i mentioned.

As I know,  u can calculate the properties (1 2 3 and 6 u  mentioned ) using Gaussian. but I am not sure about others.

Mr. Khattab,

4 and 5 also can be calculated by Gaussian. There ar etwo questions, however. Firstly, have you any background knowledge about the methods of the quantum chemistry? Secondly, have sou GaussView for Gaussian input-files?  

Dear Bojidarka,

About this line, I have a question: With the formulas, it is possible to calculate with cluster models or embedded clusters? Or it is better with periodic models?

Thank you very much

Ms. Bojidarka,

I have background about (opt, freq, raman, NMR) calculations. 

yes, i am using gaussview for input preparation and output visualization.

Mr. Khattab,

So, for points 1-3 in your posting you should use 'TD' test performed after an optimization of the geometry in the ground state (by Opt test) (points 1,3). CIS calculations for singlets and triplates (point 2). Opt of Sn states (point 3). NBO test for points 4 and 5. Freq=Raman test for point 6 using DFT or only 'Freq' using HF theoretical levels again applied after Opt test in the ground state. For computations in solution you may employ PCM for example along with TD, NBO or Freq tests. 

Those are general notes.

If you have any concrete examples of problematic inputs to all points 1-6, it would be more useful to discuss them.    

Mr. Bartra,

The answer to your question can be extracted if we pay attention to Figs 1, 1a and 2 (attachment).

The Figs. 1 and 2 represents real UV-spectra (in absorption), where to the spectrum 1 is applied baseline correction (resulting spectrum in Fig. 1a).

Each absorption spectrum is obtained as a result of interaction of the electromagnetic light with a molecular system, where the last system from an energy state Eo (ground state) is excited to another, higher, energy state (E1) (Fig. 3). After a definite period of time, this excited system returns back into the ground state. Each electronic energy level has series vibrational and rotational sub-levels. For this reason a real absorption spectrum has series of "discrete" in math term, transitions, illustrated in Fig. 2 for example, where is shown the UV-spectrum of benzene. The energies of those levels are determined by the molecular structure of the any molecular object as whole. The maximum of this function is lmax, which is proportionable to 1/nimax; or proportionable 1/E, where E values are same energy values depicted in the Fig. 3.

Given that, if you focus your attention on UV-band (Fig. 1a, ca. 210 nm) it is isolated, single band, than this spectroscopic pattern can be approximate by a Gaussian function, for example, because of it is symmetric, by contrast to IR - or Raman frequencies. However if we have hypothetically described the Gaussian function as periodic one, but, within the frame of only one cycle, due to above mentioned reasons; and if this period is -p/p, for example, than the function should be "0". But you could transform this Gaussian function into a periodic one via smoothing. An example would be shiftable-steerable Gaussian-Fourier basis. Another possibility to involve periodic function would be via multi-parameter Dirichlet functions.

In this context, where you find clusters in shown model, describing UV-absorption spectroscopic phenomena, furthermore, clusters having similar properties and thus allowing their combination in set of math cluster objects?

The electronic properties, as was written above, is determined within the frame of a given molecular structures accounting to all structural fragments. So that the energy profile (Fig. 3) is specific to given molecule. Particularly illustrative to this is the vibrational spectroscopy, rather than UV-VIS one, because of IR/Raman modes are not so broad and overlapped than the maxima in the UV-spectra. But, any individual molecule has strongly individual energy profile, meaning "spectrum".

Thanks so much!

Dear Sai

Gaussian 09 doesn't have option for dielectric constant calculation but if you go for Material Studio software then I think it might be helpful  for you. 

or VASP.

Dear Dr Bojidarka,

Plz, find attached the steps required for fluorescence spectrum determination.I hope these steps are complete and true. could you please revise it specially the molecular geometries used in each step? 

Hi Khaattab,

There should be 2 more steps in the process of fluorescence. There are two approaches (Linear Response and state specific ) to obtain absorption and emission. step 2 and 3B (NonEq=read step) give absorption in LR and SS approaches respectively. Step 4 and 6 give emission values in LR and SS respectively. Probably This is will give you some idea.

I am googling now to understand the difference between LR and SS. but my main problems will be 1) which molecular geometries i should use in every step 2) root=?? which excited state i should chose

Take ground geometry for absorption (for step 2 as well as step 3) and take step 2 checkpoint file for step 4 (Root=1). It is clearly mentioned in the Gaussian web link (http://www.gaussian.com/g_tech/g_ur/k_scrf.htm).or you follow attached pdf of Gaussian Tutorial for Fluorescence. I have highlighted the old/new chk files so you will be able to understand this now. You can choose what ever the excited state you are interested. Root=1, where ONE(1) indicates first excited state. I hope your doubts are clear now.

Dear Bojidarka B. Ivanova, what is the difference between static dielectric constant and dynamic dielectric constant? How these two can be calculated using Gaussian 09?

How can we calculate dielectric constant and susceptibility of a molecule in a gaussian03? we have dipole moment, polarizability and hyperpolarizability.