Dear Mustafa,

Generally, if an accurate optimization of the molecule is done with a relatively high basis set, the expectation is an excellent correlation between the IR & Raman calculated spectra and their corresponding experimental spectra is mmenent. I have read several papers comparing IR & Raman calculated and experimental spectra and found them to be quite similar. The following links contain some of those publications. Please note that slight change in the peak intensity or the position of the peak might happen when comparing calculated to experimental values which might be attributed to solvent effect. Some times you see more peaks for the experimental spectrum compared to the calculated one and in other cases the picture seen is the opposite. 

The following publications will give you a clear picture on the correlation and overlapping of the IR & Raman calculated and experimental spectra:

1-FT-IR, FT-Raman, UV spectra and DFT calculations on monomeric and dimeric

structure of 2-amino-5-bromobenzoic acid

Mehmet Karabacak∗, Mehmet Cinar

https://www.researchgate.net/publication/51863950_FT-IR_FT-Raman_UV_spectra_and_DFT_calculations_on_monomeric_and_dimeric_structure_of_2-amino-5-bromobenzoic_acid

Please see Figure 3 in page 594 and Table 2 in page 595.

2-Experimental and theoretical study of IR and Raman spectra of

tetraoxa[8]circulenes

Valentina A. Minaevaa, Boris F. Minaeva,b,∗, Gleb V. Baryshnikova, Hans Ågrenb, Michael Pittelkowc

Please see Figure 3 in page 159 and Tables 2-3 in 163-164.

https://theochem.kth.se/publications/attachments/2451.pdf

3-Experimental IR and Raman Spectroscopy and DFT Methods Based Material Characterization and Data Analysis of 2- Nitrophenol

Dixit V* and Yadav RA

http://www.omicsgroup.org/journals/experimental-ir-and-raman-spectroscopy-and-dft-methods-based-materialcharacterization-and-data-analysis-of-2-nitrophenol-2167-0501-1000183.php?aid=58912

Hoping this will be helpful,

Rafik

Article FT-IR, FT-Raman, UV spectra and DFT calculations on monomeri...

Maybe the compound in experiments is not the same as the one in theoretical calculations - perhaps it is unstable. Do you have any other experimental data (NMR, X-ray) which can confirm the structure ?

there are many factors affecting on disapperance of peaks like weak peaks and combination of peaks ....try to read a textbook about this subject.

Dr.Mohammad