Accurate Thermochemistry for Main-Group Elements up to Xenon with the W<i>n</i>‑P34 Series of Composite Methods

In
the present study, we introduce the accurate Wn-P34
quantum chemistry composite methods with applicability to heavy
p-block elements up to xenon. For a set of thermochemical properties
for prototypical third- and fourth-row species and for a diverse set
of small light-main-group species, they show accuracies of ∼3
kJ mol–1 or better. Overall, the Wn-P34 methods are comparable in accuracy to Wn, with
a widened applicability to heavier elements. We have used Wn-P34 to compile the P34 set of accurate thermochemical
values for heavy p-block species, and we have applied this set to
assess a wide range of lower-cost methods. The results of our assessment
show that the G4­(MP2)-XK composite method provides adequate treatments
for these species, but several widely used double-hybrid density functional
theory (DH-DFT) methods show uncharacteristically large deviations.
In contrast, we find it presently surprising that some pure and hybrid
DFT methods such as TPSS and SCANh perform quite well. We hope that
our findings and new tools would facilitate the application of computational
chemistry for heavy elements, of which the properties are yet to be
broadly explored.