Among the various types of investigations spectroscopies are the most powerful tools, allowing direct detection of different binding schemes and three-dimensional (3D) conformation via microwave (MW) measurements or indirect analysis through finger-print vibrational features in infrared (IR), Raman, Resonance Raman, UV-vis or fluorescence spectra, including also their chiral counterparts. These sophisticated experiments call for accurate and reliable theoretical support in order to link the rich experimental data to the desired information on the structure and properties of complex molecular systems.<br/>In this respect density functional theory (DFT) is nowadays a method of choice for theoretical studies of medium-to-large molecular systems. However, application of DFT to computational spectroscopy imposes additional requirements on the accuracy of DFT functionals. Focusing on the ground electronic state and flexible molecular systems, these are the accurate predictions of (i) equilibrium and vibrationally averaged molecular structures, (ii) free energies of different conformers for specific experimental conditions, and (iii) harmonic and anharmonic vibrational properties.<br/>In this work performance of widely used dispersion-corrected DFT approaches and double-hybrid DFT models will be discussed with respect to highly accurate theoretical results of CCSD(T)/CBS quality and available spectroscopic data relevant for accurate characterisation of entire conformational flexibility of bio-molecules building blocks.

Density functional theory for spectroscopy and thermochemistry

255th National Meeting (2018)

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