In order to compare the density functional theory (DFT) and the method with the molecular valence connectivity index of the 3rd order (3χv) in the estimation of stability constants log β2, we used copper(II) complexes with thioflavin-based intercalation compounds designed for application in Alzheimer's disease. Correlation of ten log β2 values calculated by DFT with 3χv yielded r=0.988 and S.E.=0.85. The correlations of indices I(NG), HOMA and 3χv with log β2, and the intercorrelations between the indices revealed the crucial influence of 3χv on the prediction of the stability of these complexes.