Addressing anharmonic effects with density-fitted multicomponent density functional theory

In this contribution we present a new density-fitted multicomponent density functional theory implementation and assess its use for the calculation of anharmonic zero-point energies. Four challenging cases of molecular aggregates are reviewed: deprotonated formic acid trimer, diphenyl ether-tert-butyl alcohol conformers, anisole/methanol and anisole/2-naphtol dimers. These are all cases where a mismatch between the low-temperature computationally predicted minimum and the experimentally determined structure was observed. Through the use of nuclear-electronic orbital energies in the thermodynamic correction, the correct energetic ordering is recovered. For the smallest system, we compare our results to vibrational perturbation theory anharmonically corrected zero-point energy, with perfect agreement for the lower-lying conformers. The performance of the newly developed code and the density fitting errors are also analysed. Overall, the new implementation shows a very good scaling with system size and the density fitting approximations exhibit a negligible impact.