  In the paper commented on [J. Chem. Phys. 130 (2009) 144102], Cheng et al.
derived a formula for the magnetic dipole shielding constant $\sigma$ for the
Dirac one-electron atom in its ground state. That formula involves an infinite
series of ratios of the Euler's gamma functions. We show that with some algebra
the series may be expressed in terms of elementary functions. This leads to a
simple closed-form expression for the shielding constant.
