According to the Bader's definition, vdW radius can be defined as distance between nucleus and a point on the isosurface of rho=0.001. Based on this definition, you can use Multiwfn (//www.umsyar.com/multiwfn) to calculate atomic radius easily.

As an example, we calculate radius for Ar, the needed wavefunction file has already been provided in Multiwfn package. Boot up Multiwfn and input below commands

examples\atomwfn\Ar.wfn
12
6
10
1
You will see:
The farthest distance to the point: 3.735141 Bohr ( 1.976552 Angstrom)

That means the vdW radius can be regarded as 1.976 Angstrom.

For silver and its ion, you can use such as Gaussian to generate .fch/wfn/wfx file, which can be used as input file for above analysis to derive their radii.