Multicomponent Double-Hybrid Density Functional Theory.

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Density Functional Theory (DFT) is a powerful tool for electronic structure calculations.
• Multicomponent DFT (NEO-DFT) extends DFT to systems with light, mobile nuclei.
• Improving the accuracy of electron-proton correlation in DFT remains a challenge.

Purpose of the Study:

• To investigate the improvement of multicomponent DFT results by including Møller-Plesset (MP) perturbation theory electron-proton correlation energies.
• To develop and parametrize new DFT models by combining DFT with MP2 correlation.
• To evaluate the performance of these new models on chemical systems involving proton transfer.

Main Methods:

• Exploration of three formulations based on double-hybrid functionals (B2PLYP, DSD-PBEP86, PBEQIDH).
• Parametrization of the DFT/MP2 correlation energy ratio using the PA23 proton binding affinities dataset.
• Evaluation of the models on a set of titratable molecules and specific chemical systems like protonated water hexamers and a crown ether molecule.

Main Results:

• The combination of NEO-DFT and MP2 electron-proton correlation reduced the root-mean-square deviation (RMSD) by up to a factor of 2 compared to standard NEO-DFT.
• A DFT/MP2 ratio of approximately 0.8:0.2 demonstrated robust improvement across different models and basis sets.
• The parametrized NEO-B2PLYP model was successfully applied to study protonated water hexamers and proton dynamics in a crown ether.

Conclusions:

• Admixing MP2 electron-proton correlation energies significantly enhances the accuracy of multicomponent DFT calculations.
• The developed models provide a robust improvement for predicting molecular energetics, particularly in systems with proton transfer.
• The findings offer a more accurate computational approach for studying complex chemical phenomena involving protons.