Abstract
In a recent paper [A. B. Volkov, Phys. Rev. A 39, 4406 (1989)] the square of the Dirac Hamiltonian matrix built within a finite-basis-set representation is used to obtain variational solutions to the Dirac equation. We show in this Comment that no advantages are gained by the use of this method that is in fact equivalent to the diagonalization of the nonsquared Dirac Hamiltonian. Most importantly one does not avoid the problems of variational collapse and spurious roots. A simple example is given showing that the method proposed in this work fails to provide bounds to the ground state of hydrogenic ions.
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