Models of statistic sums for atoms and molecules

The problem of statistic sums restricting for H-like ions is reviewed. The attention is mainly paying for microfield influence; there is obtained corresponding formfactor. The earlier–known formfactors are also compared with experimental data on spectra. One can see, that microfield formfactor explain very well the last experiments in wide area of temperatures and densities, and this one is the best of all models mentioned. The simple formulas for statistic sums computation with this formfactor are given; they are very convenient for practical calculations. The influence of choice of molecular interaction's potentials on values of statistic sums is investigated. The highly accurate simple approximate statements for sums with “GOHR” and Morze potentials are given.