Construction of potential curves for diatomic molecular states by the IPA method. A. Pashov, W. Jastrzebski, P. Kowalczyk.

Title of program: IPA, SCHROED
Catalogue identifier: ADLV
Ref. in CPC: 128(2000)622
Distribution format: zip file
Operating system: MS DOS
Peripherals Required: disc
Number of lines in distributed program, including test data, etc: 11581
Programming language used: Fortran
Computer: IBM PC, Pentium 90

Nature of physical 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.

Method of solution
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 on the complexity of the program
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.

Typical 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.