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Manuscript Title: Construction of potential curves for diatomic molecular states by the IPA method.
Authors: A. Pashov, W. Jastrzebski, P. Kowalczyk
Program title: IPA, SCHROED
Catalogue identifier: ADLV_v1_0
Distribution format: zip
Journal reference: Comput. Phys. Commun. 128(2000)622
Programming language: Fortran.
Computer: IBM PC, Pentium 90.
Operating system: MS DOS.
Peripherals: disc.
Keywords: Molecular physics, Structure, Potential curve, Diatomic molecules, IPA and RKR methods.
Classification: 16.1.

Nature of problem:
This program constructs an accurate potential curve of a 1Sigma or a 1Pi state of a diatomic molecule from given energy levels of the state observed experimentally.

Solution method:
The radial Schrodinger equation is solved with an approximate potential and zeroth-order eigenvalues and wave functions are obtained. In the next step, using the first order perturbation theory we seek a correction to the approximate potential that minimizes the difference between the observed and the corrected energy levels.

Restrictions:
The approximate potential U0(R) and the correction to it deltaU(R) are defined in numerical form as arrays of points. Points of deltaU(R) must be equidistant in R. The addition of U0(R) and deltaU(R) is performed by the user.

Running time:
The running time depends on the total number of energy levels and the number of points of deltaU(R). Fitting of a potential in a typical case (1000 levels, 20 points) requires several minutes.