Saturday, March 15, 2014

Diamond: Electronic Ground State of Carbon at Temperatures Approaching 0 K

Highlighted by François-Xavier Coudert

Is graphite a true “ground state” of carbon not at “standard conditions” (p = 1 atm, T = 298 K) but—less arbitrarily—at p approaching 0 atm, and T approaching 0 K? And how do the thermodynamic contributions to the stability of both allotropes evolve? Here we attempt to get insight into the relative stability of graphite and diamond with the use of state-of-the-art hybrid density functional theory (DFT) methods, compare the results obtained with the comprehensive set of experimental data available, and discuss the discrepancies.
There are cases where a paper is so clearly written that it does a pretty good job of highlighting itself.  This quote above (emphasis is mine) does a pretty good job of explaining the problematic of the paper to a lay audience.

The results of the author's calculations (using HSE06/PBEsol) show that diamond actually has lower electronic energy than graphite, while the zero-point energy contribution favors graphite, bringing the two polymorphs to near-degeneracy. The vibrational contribution to entropy also favors the graphite phase, though the harmonic approximation leads to a large difference with the experimental entropy at 298 K.