The CUAGAU Set of Coupled-Cluster Reference Data for Small Copper, Silver, and Gold Compounds and Assessment of DFT Methods

We have obtained benchmark data for
a set of small molecular systems
of Cu, Ag, and Au using coupled-cluster methods. Using this collection
of reference data (that we termed the CUAGAU set) for assessing DFT-type
methods, we find the MN15-L nonhybrid DFT to be cost-effective for
geometry optimization [mean absolute deviation (MAD) in bond length
= 0.20 Å], with an accuracy that is comparable to that for the
double-hybrid (DH) DFT method DSD-PBEP86 (MAD = 0.19 Å). For
the computation of thermochemical properties, among “conventional”
(non-MP2-based) DFT methods, the best performance is found for the
global-hybrid meta-GGA functional MN15, with an MAD of 11.4 kJ mol–1. We also find the nonhybrid method B97M-rV to have
a reasonable performance (MAD = 14.4 kJ mol–1),
and it may serve as a cost-effective means for qualitative study.
If we look beyond conventional functionals, we find DSD-PBEP86 (MAD
= 7.3 kJ mol–1) to be more accurate than even MN15.
Nonetheless, this level of accuracy is still not sufficient for quantitative
studies. In this regard, high-level wave function methods such as
composite procedures that are based on coupled cluster are still indispensable
for obtaining reliable reference data for transition-metal species.