On assessing functional errors in density functional theory using atomisation energies and electric field gradients

Abstract

Despite the exact form of E xc being unknown, remarkably simple approximations can provide unrivaled accuracy to cost ratio. Both physically and empirically motivated approaches for developing E xc are used, but nearly all focus upon improving calculated energies. Herein we simultaneously study energy and density errors associated with a range of density functionals for CuCl and four related complexes. Atomisation energies are compared with high-level coupled cluster, CCSD(T), while computed electric field gradients are compared with those obtained from microwave spectroscopy and CCSD(T). We show that simple metrics are able to reveal the relative contributions of the energetic errors associated with the use of an approximate density and an approximate exchange and correlation functional. The methods adopted provide a potentially useful approach for assessing and developing new balanced functionals that are able to provide simultaneous improvement in both energetics and properties associated with the electron density.

Density-Corrected Density Functional Theory for Molecular Properties

“…The TM systems TiO, NiH, and CuCl likely belong to the second category as well. Certainly, CuCl is known to be an extremely challenging case for EFG calculations with DFAs. − …”

“…The EFGs of the atoms in CuCl are infamous for being challenging cases for DFAs. ,− For a given, fixed Cu–Cl distance, and when conceptualizing the formation of a partially covalent bond starting from spherical Cu + and Cl – ions, the electronic contributions to the EFGs, and their errors, are driven by the extent of the Cl – → Cu + donation. It was shown previously that the DE is responsible for the large variations among the calculations.…”