metallic_region1 = SphereRegion(
    value=1.0*Volt,
    radius=2.0*Angstrom,
    center=[1.0, 2.0 ,3.0]*Angstrom
)

metallic_region2 = metallic_region1(
    value=-1*Volt,
    radius=3.3*Angstrom,
)