metallic_region1 = TubeRegion(
    value=1*Volt,
    start_point=[1.0, 2.0, 3.0]*Angstrom, end_point=[4.0, 5.0, 6.0]*Angstrom,
    inner_radius=3.5*Angstrom,
    thickness=1.2*Angstrom
)

metallic_region2 = metallic_region1(
    value=-1*Volt,
    inner_radius=1.1*Angstrom,
    thickness=0.5*Angstrom
)