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.

Acknowledgement

We thank NSERC (Canada) for financial support for this work, via Summer Student Research Awards to C.R. and L.C., and a research grant to J.S.W.