ΔDFT/MIX: A reliable and efficient method for calculating core electron binding energies of large molecules

A new method, ΔDFT/MIX, is calibrated for use in calculating core electron binding energies. Chemically relevant test sets were used to determine the most accurate functionals out of the 70 density functionals included in GAMESS. The best three functionals, B3LYP, TPSSm, and BLYP, were used to calculate 1s electron binding energies of nucleic acid base tautomers, and the results were compared to experimental values to demonstrate accuracy and sensitivity of the method. Previously suggested methods such as ACD(4) and ΔMP2/MIX are as accurate as our new method; the overall mean absolute deviation of ΔDFT/MIX is 0.19 eV with B3LYP. Comparing calculation time shows that using DFT instead of MP2 is much less computationally costly for larger molecules.