Design of new family of minimal parameter spin-component-scaled double-hybrid density functional theory

Presently, Kohn-Sham density functional theory (DFT) is one of the most established theoretical methods due to its highly favorable system size to computational cost and inherent treatment of electron correlation. Conversely, this success critically depends on the quality of the exchange-correlation function. Recent scientific advances have seen the development of several techniques aimed at overcoming shortcomings in the treatment of weak interactions with the GGA functionals, which have a direct impact on the properties of a wide range of applications, including proteins folding, crystal packing motifs, and encapsulation energies in nanostructures. The double-hybrid scheme has shown to be a promising strategy for accurate representation of correlation effects. More specifically, dispersion-corrected spin-component-scaled double-hybrid, spin-opposite-scaled double-hybrid, and quadratic integrand double-hybrids, are of particular interest as they reach chemical accuracy. Unfortunately, there are still a number of features that result in an unphysical representation of the correlation effects, most notably the overweighting of the correlation contribution to the total energy of the functional in these methods.

Dr. Loïc Roch and Professor Kim Baldridge at University of Zurich in Switzerland addressed the major drawbacks of the general dispersion-corrected spin-component-scaled double-hybrid DFT methodology through the design of a new family of functionals, referred to as minimal parameter spin-component-scaled double-hybrid, or mSD-DFT. They anticipated that this methodology could retain a 0.5 kilocalorie per mole target accuracy, eradicate the unphysical correlation contributions, and provide a class of approaches with negligible empiricism. Their work is now published in the research journal, Phys.Chem.Chem.Phys.

The authors observed that for the specific case of mSD-PBEPBE, the mean absolute error was 0.4 kilocalorie per mole, which was within the chemical accuracy target. Moreover, with only two parameters, which are extrapolated to the complete basis set (CBS) limit, this novel family of double-hybrid DF ensures limited empiricism.

An important outcome of the work of Loïc Roch and Kim Baldridge is a generalized procedure towards the design of a new family of double-hybrid, referred to as mSD-DFTs. Their procedure is shown to be robust and lead to functionals that are relatively insensitive to  small variations in the parameters around the extrapolated minimums. Additionally, the mSD-DFT scheme was shown to be extendable to include the resolution of identity approximation for solving the computationally intensive integrals. This cost-effective counterpart, referred to as RI-mSD-DFT, drastically reduces the computational cost and resource usage to enable extension to large chemical and biological systems, for investigations of real-life chemical challenges. The scheme can therefore be recommended for the design of additional (RI-)mSD-DFT methods based on others of the plethora of density functional theory types. In fact, having a broader range of such functionals will enable a more thorough comparison of performance of this new family of double-hybrid density functional theories.