A novel interpretation of min-max theorem and principle in relativistic quantum chemistry.

[Display omitted] • Rosicky-Mark variation optimizes u-l coupling in 4-spinor, creates energy maximum. • Variation of maximum with constrained component u (or l) gives an upper bound. • Steps together was named constrained component variation, is same as the min–max. • A new interpretation is that the coupling constraint restores Lorentz covariance. The development of min–max theorem and min–max principle for solving wave equations in relativistic quantum chemistry is briefly discussed. A new interpretation of the min–max treatment of Dirac equation is suggested. The min–max restores covariance in a one-electron formalism and tries to find a pure state. [ABSTRACT FROM AUTHOR]