In order to obtain optimized geometries and calculate free energies at reduced cost, it is common for computational chemists to optimize structures at a relatively inexpensive level of theory (e.g. using a small basis set, or ignoring solvent effects) and then re-calculate the electronic energy with a single-point calculation using a more accurate and expensive level of theory (e.g. using a larger basis set or including an implicit solvent model). There are therefore two natural ways to calculate molecular thermodynamics: one in which all thermodynamic quantities of interest (electronic energy, enthalpy, entropy, etc.) are calculated from a single vibrational frequency analysis calculation, and another in which most properties are obtained from a vibrational frequency analysis but the electronic energy is instead obtained from a single-point energy calculation performed on the same structure at a higher level of theory.