  As the only semimetallic $d^{10}$-based delafossite, AgNiO$_2$ has received a
great deal of attention due to both its unique semimetallicity and its
antiferromagnetism in the NiO$_2$ layer that is coupled with a lattice
distortion. In contrast, other delafossites such as AgCoO$_2$ are insulating.
Here we study how the electronic structure of AgNi$_{1-x}$Co$_{x}$O$_2$ alloys
vary with Ni/Co concentration, in order to investigate the electronic
properties and phase stability of the intermetallics. While the electronic and
magnetic structure of delafossites have been studied using Density Functional
Theory (DFT), earlier studies have not included corrections for strong on-site
Coulomb interactions. In order to treat these interactions accurately, in this
study we use Quantum Monte Carlo (QMC) simulations to obtain accurate estimates
for the electronic and magnetic properties of AgNiO$_2$. By comparison to DFT
results we show that these electron correlations are critical to account for.
We show that Co doping on the magnetic Ni sites results in a metal-insulator
transition near $x\sim 0.33$, and reentrant behavior near $x\sim 0.66$
