Dear Prabhjot Kaur

The scale of experimental results depends on many parameters like concentration, and on the other hand when you convert your calculated oscillator strength to UV/Vis spectra you convolute your results with a Gaussian broadening, and changing FWHM in your gaussian functions affects the shape of your spectrum.

Then one practical approach to compare the theoretical results from TDDFT with those of experiments is renormalizing your results to have the same first peak heights on experimental and theoretical curves.

However, employing different XC functional can cause a notable shift in the position, and even the number of peaks in a given range of energy and you should take this into account.

good luck

I second Yavar's comment. Just a little addition to that. Usually if you have literature on similar chemical systems you might already recognise the strongest electronic transitions of your system. Your functional groups with shift the spectrum either batho or hypsochromically. You can shift the spectrum by a constant factor which you can set from your observation. However you need to keep this factor constant for all calculations you perform and report it if you write an article. Secondly as Yavar mentioned, some Gaussian broadening is a must. Thirdly, you can choose how many transitions you want to compute and that determines the range of the x-axis. Also, if these calculations are performed with chosen solvent shell then your results have a better match with the experiment. Usually you normalize the spectrum by setting the absorption of the most pronounced transition to 1. Best of luck.

Thank you @Yavar Taghipour

Thank you @ Saunak Das. Yes I have normalized the most pronouced transition to 1.

Dear Prabhjot Kaur ,

I could suggest you to see this excellent publication on this subject for representation of calculated UV-Vis spectrum with the experimental :

https://www.sciencedirect.com/science/article/abs/pii/S0166128010003180

You use origin software for plotting spectra and see tutorial on YouTube.