RELATIVISTIC QUANTUM-CHEMISTRY AND RIGOROUS VARIATIONAL ANALYSIS

A brief review of relativistic quantum chemistry is given here. Relati vistic effects and their importance in chemistry are discussed. An out line of different theoretical aspects is presented. Aspects of variati on techniques relevant to relativistic calculations are discussed in d etail. These involve the derivation of min-max theorems for Dirac, Dir ac-Hartree-Fock and Dirac-Coulomb calculations. The consequence of rel ativistic Hamiltonians being unbounded are also discussed for other li nes of investigation. The upper bounds derived are physically interpre ted. Sample Dirac-Hartree-Fock results for the Be atom, calculated usi ng both STO and GTO bases for the nonrelativistic orbitals and the upp er components of the relativistic orbitals, are given. The inadequacy of the so-called kinetically balanced basis set is discussed and illus trated with these results. The importance of the variational or dynami cal balance and hence the merit of the LCAS-MS scheme is pointed out. The possibility of calculating quantum electrodynamical pair energy fr om relativistic configuration interaction calculations on a two-electr on atom is discussed and exemplified. The present status of relativist ic molecular calculations is briefly reviewed. Conclusions on the aspe cts of variational analysis and molecular calculations are enclosed.