The PACO (popularity adapted consensus object) functional is a weighted density functional based on an annual popularity poll organized by the Institute of Computational Chemistry of the University of Girona, Spain.
Density functional theory (DFT) results can greatly vary depending on the functional chosen. “The aim of the popularity poll is to probe the preferences of the computational chemistry community, and compile the quality of the ‘average’ DFT computation.” according to the online competition’s organizers. A voter can “like” functionals for positive points or “hate” them for a negative point.
At the end of polling, the functionals with more points are weighted to compile the popularity adapted consensus object (PACO) functional. PACO is then applied to typical chemical systems with specific applications: AE6 set for atomization energies, BH6 set for barrier heights, π-π stacking energy, spin-state splitting, excitation energies, and hydrogen-bond energies. These systems were chosen because they have high-level ab-initio (e.g. CCSD(T)) or experimental data available to compare with the results from the “consensus-built” PACO functional.
In both, 2010 and 2011, the parameter free density functional model (PBE0) was voted the most popular functional.
The 2012 voting began at the start of June and runs until October 1, 2012. Thereafter the ranking of density functionals for the year 2012 will be made.