The current research deal with ab initio calculations of equilibrium constants of stability or dissociation and some spectral properties of 2-thiobarbituric and barbituric acids. 11 DFT functionals (revTPSS, TPSSh, PBE, revPBE, M06-L, M06, M06-2X, M05-2X, M06-HF, CAM-B3LYP, X3LYP) with cc-pVDZ basis set were used for calculations of
and
. For each of functionals the calculations were carried out for three solvation models – SMD, COSMO and C-PCM. It has been found that functionals containing 55% Hartree-Fock exchange (M06-2X and M05-2X) provide a better approach. The TD-DFT calculations show that revTPSS and TPSSh give accurate results for the description of the spectral characteristics. The revTPSS/CRNBL ECP/SMD level was tested for evaluating parameters of complex formation process these acids with La(III) for various computational models.