Finding the energies of bound states of screened Coulomb potentials has raised considerable interst for many years. There are many problems for which the reduction of the long-range Coulomb interactions due to the screening can drastically affect the results emerging from the consideration of bare Coulomb potentials. Thus, the calculation of thermodynamic properties of many-body systems in partially ionized gases, i.e., plasmas, has seen a rebirth since the inclusion of screening effects. The screened Coulomb potential can be represented by different models, the most famous of which is the analytic exponentially decaying potential of Yukawa type, shown in Figure 1.

 
Figure 1. The Coulomb potential (-1/r) lower curve and the Yukawa potential (-exp(-lr)/r), upper curve.

In spite of the importance of the Yukawa potential, it has been only scarcely studied. Part of the problem is due to that even for the hydrogen molecule the corresponding Schrodinger equation cannot be solved analytically, hence calculations must rely on approximate methods.

We have been able to solve analytically all the basic molecular integrals for the Molecular Orbital Theory implementation of the Yukawa potential problem and, cast them into a suitable code form. Our molecular integrals package is currently interfaced with the GAMESS package and is working for all the features provided by GAMESS. Please refer to the Publications section for more information or drop us a note if you are interested in obtaining a copy of the program.