Programs in Physics & Physical Chemistry
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|Manuscript Title: COULN: a program for evaluating negative energy Coulomb functions.|
|Authors: C.J. Noble, I.J. Thompson|
|Program title: COULN|
|Catalogue identifier: ACCU_v1_0|
Distribution format: gz
|Journal reference: Comput. Phys. Commun. 33(1984)413|
|Programming language: Fortran.|
|Computer: NAS 7000.|
|Operating system: MVT.|
|RAM: 650K words|
|Word size: 8|
|Keywords: General purpose, Coulomb, Whittaker, Continued fraction, Pade, Asymptotic, Molecular physics, Theoretical methods.|
Nature of problem:
Program COULN calculates exponentially decaying Whittaker functions, Wkappa, mu(z)corresponding to negative energy Coulomb functions. The method employed is most appropriate for parameter ranges which commonly occur in atomic and molecular asymptotic scattering problems using a close-coupling approximation in the presence of closed channels.
The asymptotic series for the Whittaker function is analytically continued using a continued fraction representation devised by Nesbet. Functions corresponding to higher orbital angular momenta are computed by recursion.
Program COULN assumes real negative energies, E = - |k|**2, non-negative real values of orbital angular momenta, l (integer), and separations, r. The charge product, Z, must be non-zero. The method becomes less efficient for large values of |Z| and small values of the product Z = |k|r. It is suitable for z/Z greater than 0.5 on IBM computers and greater than 0.1 on the CRAY-1S in double precision.
The test run required 5.2 s on the NAS 7000.
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