Hulthen-Kohn variational principle

Variational principles play an important role in the solution of the Schrbdinger equation, e.g. the Ritz-method [5] for the solution of partial differential equations and the Rayleigh-Ritz method [6] for the calculation of bound states of atoms and molecules. The oldest variational method for scattering problems was introduced 1944 by Hulthen [7]. Four years later Hulthen and Kohn [8, 9, 10] independently developed what is now known as the Hulthen-Kohn... 

S-matrix version of the Hulthen-Kohn-variational principle... 

Derivation in one dimension. To make the derivation simpler everything will now be formulated in one dimension. In order to derive the S-matrix version of the Hulthen-Kohn variational principle (HKVP) one uses trial functions with incoming and outgoing wave boundary conditions [15, 16, 22] ... 

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