  We propose an improvement of the basis for the solution of the stationary
two-centre Dirac equation in Cassini coordinates using the finite-basis-set
method presented in Ref. [1]. For the calculations in Ref. [1], we constructed
the basis for approximating the energy eigenfunctions by using smooth piecewise
defined polynomials, called B-splines. In the present article, we report that
an analysis of the employed representation of the Dirac matrices shows that the
above approximation is not efficient using B-splines only. Therefore, we
include basis functions which are defined using functions with step-like
behaviour instead of B-splines. Thereby, we achieve a significant increase of
accuracy of results as compared to Ref. [1].
