Sometimes, the oscillation strength value from excited state calculation results can be used to compare molar absorption coefficients in experiments. However, it cannot show perfect description. It cannot perfectly well describe the real nature of transition.
I need to know how to calculate exact transmittance spectrum from a TDDFT calculation or other methods. Is there someone who knows or has some ideas about this problem? I've searched many times by google or papers but I never found any clues for solving this problem.
Keep in mind the following: if a sample is in its solid state, when the incoming light(I0) reaches it, you will have reflection(R), absorption(A) and transmission(T), so that I0 = R+A+T.
In molecular systems, we often neglect the reflection, as you may confirm by looking the technical specifications of some commercial absorption spectrometers. In this case, I0 = A+T, and what is really measured is the transmittance divided by I0.
In order to compare, as TDDFT results are normalized, A+T=1, you can simply do T=1-A, and it is necessary normalize the experimental data for a better comparison.
The relationship A = f(T) in optical spectroscopy is given by the A = lg(100/T(%)), because of A = lg(I0/I) and the T = (I/I0).100 in %. The I0 is namely the intensity of the incoming light. A-absorptiona nd T - transmittance
Thanks all your answers.
I've already known about relationship between transmittance and absorption coefficient. I think i cannot well write sentence what i want to ask you guys. Thiis is totally my fault. Very sorry you guys.
My questions are following as
(1) Is there any specific method (or code) to perform only transmittance calculation?
(2) Sometimes, the oscillation strength values for different molecules cannot well match with experimental results (molar absorption coefficients). Thus, is there any way to improve obtaining exact oscillation strength??
Mr./Miss/Mrs. Kang, as far as the f is proportional of the absolute value of the electric dipole moment (mu) of a given 'ab' transition absorbing the electromagnetic light. Each factors affecting mu, therefore is joined with the accuracy of f prediction. Especially solute-solute and solute-solvent interactions. Actually highly accirate data are obtained when the theoretical levels are maximal appropriate to given molecular system and the environment (calculations in solution). In this respect the PCM and C-PCM are highly recommendable. Please find related refs and all other ones included in these papers:
1. M. Cossi, N. Rega, G. Scalmani, V. Barone, , Energies, Structures, and Electronic Properties of Molecules in Solution with the C-PCM Solvation Model, Journal of Computational Chemistry, 2003, 24, 669
2. J. Tomasi, B. Mennucci, R. Cammi, Quantum Mechanical Continuum Solvation Models, Chem. Rev. 2005, 105, 2999-3093
3. B. Mennucci, J. Tomasi, R. Cammi, J.Cheeseman, M.Frisch, F.Devlin, S. Gabriel, P.Stephens, Polarizable Continuum Model (PCM) Calculations of Solvent Effects on Optical Rotations, of Chiral Molecules, J. Phys. Chem. A 2002, 106, 6102-6113
Towards the A-in-T code/transformation you do not need. It is very simple math procedure. Even if you have exp spectra in T, they can be very easy transform in A and compare to the theoretical data.
First of all you can not calculate the exact absorbance or transmittance from calculations. Because you do not know the exact bandwidth. Therefore, first you must use an arbitrary bandwidth, then you divide the calculated values to the bandwidth at half-height to obtain the absorbance of the peaks and transform to transmittance.
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