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The Schwinger multichannel method K. Takatsuka and V. McKoy, Phys. Rev. A 30, 1734 (1984), which is based on the Schwinger variational principle for the scattering amplitude J. Schwinger, Phys. Rev. 72, 742 (1947), was designed to account for exchange, polarization and electronically multichannel coupling effects in the low-energy region of electron scattering from molecules with arbitrary geometry. The applications of the method became more ambitious with the availability of computer power combined with parallel processing, use of norm-conserving pseudopotentials and improvement of the description of target excited states (minimal orbital basis for single configuration interaction). The most recent applications involving 33 and 45 electronically open channels for phenol and ethylene molecules, represent good examples of the present status of the method. In this colloquium, we review the strategy and point out new directions to apply the method in its full extension.
Costa et al. (Mon,) studied this question.