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

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.

Automated summary

This study uses simple approximations to improve the accuracy of density functionals, while simultaneously investigating the impact of energy and density errors in CuCl and related complexes; the results show that simple metrics can reveal the relative contributions of energy errors from approximate density and exchange-correlation functionals.