  The high-accuracy W4 computational thermochemistry protocol, and several
post-W4 methods, have been applied to the P$_2$ and P$_4$ molecules. Contrary
to previous studies, we find the experimental thermochemistry to be
fundamentally sound. The reaction enthalpy for P$_4\to 2$P$_2$ has a very
significant contribution from post-CCSD(T) correlation effects. We derive a
gas-phase heat of formation for the phosphorus atom of $\Delta
H^\circ_{f,0}$[P(g)]=75.54$\pm$0.1 kcal/mol and $\Delta
H^\circ_{f,298}$[P(g)]=75.74$\pm$0.1 kcal/mol, in the upper half of the CODATA
uncertainty interval.
