On the accuracy of frozen density embedding calculations with hybrid and orbital-dependent functionals for non-bonded interaction energies

We analyze the accuracy of the frozen density embedding (FDE) method, with hybrid and orbital-dependent exchange-correlation functionals, for the calculation of the total interaction energies of weakly interacting systems. Our investigation is motivated by the fact that these approaches require, in addition to the non-additive kinetic energy approximation, also approximate non-additive exact-exchange energies. Despite this further approximation, we find that the hybrid/orbital-dependent FDE approaches can reproduce the total energies with the same accuracy (about 1 mHa) as the one of conventional semi-local functionals. In many cases, thanks to error cancellation effects, hybrid/orbital-dependent approaches yield even the smallest error. A detailed energy-decomposition investigation is presented. Finally, the Becke-exchange functional is found to reproduce accurately the non-additive exact-exchange energies also for non-equilibrium geometries. These performances are rationalized in terms of a reduced-gradient decomposition of the non-additive exchange energy.

Towards an accurate description of the electronic properties of the biphenylthiol/gold interface: the role of exact exchange

We investigate the role of the exact exchange in describing the biphenylthiol/gold interface. The study is performed by simulating the electronic properties of mercaptobiphenylthiol and aminobiphenylthiol molecules adsorbed on a Au(23) cluster, using local, semilocal and hybrid functionals and an effective exact exchange method, namely, the localized Hartree-Fock (LHF). We find that the local/semilocal functionals strongly underestimate the charge transfer and the bond dipole at the interface due to the self-interaction-error (SIE), which alters the correct level alignment. On the other hand the LHF method is SIE free and predicts a larger charge transfer and bond dipole. We also found that LHF results can be reproduced using hybrid functionals and that conventional local/semilocal correlation functionals are unable to improve over the exchange-only description.