CONSTRAINED MINIMIZATIONS FOR THE CALCULATION OF KOHN-SHAM AND NATURAL ORBITALS

An alternative simple constraint quantity is employed in the procedure of Zhao, Q., Morrison, R. C., and Parr, R. G. (1994, Phys. Rev. A, 50 , 2138) for the calculation of molecular exchange-correlation potentia ls. The inability to represent exactly a correlated density in terms o f a Kohn-Sham density for a finite basis set leads to a very poor desc ription of the core using this constraint. A general constraint quanti ty is introduced involving the one-density which, for an infinite Lagr ange multiplier, yields either natural orbitals or Kohn-Sham orbitals depending on whether the constraint used is complete or diagonal. Resu lts are given using this procedure, although no formal connection coul d be seen between Kohn-Sham and natural orbitals.