A ‘universal’ B3LYP-based method for gas-phase molecular properties: bond dissociation enthalpy, ionization potential, electron and proton affinity and gas-phase acidity

Abstract

The paper describes a density functional theory methodology using the B3LYP functional, with small correction terms introduced for open shell doublet states and closed-shell anions. The procedure is based on a B3LYP/6-31G(d) geometry optimization and frequency determination, followed by (RO)B3LYP/6-311 + G(2d,2p) single point energy calculations. Using a correction term of +8.368 kJ mol−1 for (doublet) radicals and + 4.184 kJ mol−1 for (closed shell) anions, close agreement is obtained with experiment (i.e. within 10 kJ mol−1) for a series of molecular properties. These include bond dissociation enthalpies for X–H, where X = functional groups containing C, N, O, F, S, and X–Y, where X and Y are binary combinations of the same five heavy atoms plus Si and Cl, ionization potentials, electron and proton affinities, and gas-phase acidities. Using locally dense basis sets the approach can be extended to bond dissociation enthalpy calculations of large molecules with only a small increase in error. Using the same approach and popular solvation models allows a good starting point for reaction properties in solution. The approach is termed ’niversal' because by applying these corrections there is no need to change functionals and/or basis sets to obtain accurate results for different molecular properties, unlike some of the work reported previously.