metal-rough-glass

This shader supports transparent materials while preserving reflections. This is a modified version of the metal-rough-with-alpha-blending shader. As such an opacity channel is required in the project. Opacity drives the intensity of the effect. The luminance of the pixel to be rendered determines what's transparent versus what isn't.

Your best bet is to set your base color to black or near black. This shader fakes transparent reflections and as such I wouldn't consider it PBR, but it's good enough for preview purposes. This does not simulate refraction.