Theoretical Practices Old and New

The QRS problem poses unique challenges which make otherwise useful quantum mechanical methods fail. This difficulty arises from the multi-arrangement nature of the reactive collision event (please see Fig. 1.1). For example, although 

The first accurate cross section calculation, performed by Schatz and Kup-permann [19] in 1976 on the H+H2 reaction, involved a sufficiently complicated variant of CC propagation that its successful implementation was restricted to H+H2 at low energies (i.e. no vibrational excitation). Nevertheless, this work represented a breakthrough in QRS. Indeed, one may view as an outgrowth of this work a general coordinate system which allows straightforward reactive CC calculations. This coor- 

The ABC method reduces the scattering problem to the determination of the ABC Green s function (G), a matrix inverse. Although formally this is just as computationally demanding as full diagonalization, the initial state selected formalism only requires a single column of G. Iterative methods, which require very little core memory, can be used to compute a single column of G rapidly. We develop an iterative 

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