Comparison of Standard Functionals to Calculate the Properties of Molecules at the Variational Limit

Abstract

B1LYP, B1PW91, B3LYP, BHandH, BHandHLYP, BLYP, BP, CAMY-B3LYP, HTBS, KMLYP, LCYBLYP, LCY-BP86, LCY-PBE, LDA, M06, M06-2X, M06-HF, M06L, mPBE, mPW, MPW1K, MPW1PW, O3LYP, OLYP, OPBE, OPBE0, PBE, PBE0, PBEsol, PW91, revPBE, revTPSS, RPBE, TPSS, TPSSH, X3LYP, and HF methods are used to calculate the electron energy E_el of the reference GeO and C2H6 compounds in Slater basis sets QZ4P, aug-TZ2P, and TZ2P, as well as DZ for C₂H₆. The E_el values are recalculated into the bond breaking enthalpy D₀(Ge–O) and formation enthalpy ΔfH₂₉₈⁰ of ethane, and calculation errors for E_el are obtained at the variation limit. The ADF program settings are chosen so that they make it possible to attribute these E_el errors to the structure of DFT functionals. The dependence of the E_el values on the type (size) of the basis set is studied. It is demonstrated that when Eel is calculated for GeO, the optimum combination is DFT/TZ2P, where DFT = LCY-BLYP, LCY-BP86, LCY-PBE, CAMYB3LYP; for C₂H₆ it is DFT/TZ2P, where DFT = PBE0, M06, mPBE, OLYP. Errors in the calculation of the geometric parameters are studied.