Analytic functions for the three-body potential of the helium trimer

The three-body potential for the ground state of the helium trimer is determined by an extended geminal model. The basis set for the calculation is an uncontracted (19s,7p,6d,5f,4g,2h) set of Gaussian-type functions. Three different types of configurations were considered: (i) equilateral triangles, (ii) linear configurations with R12=R23, and (iii) a set of pseudorandom configurations. The interatomic distances were selected within the interval 3.0,9.0] bohrs. The computed points have been fitted to global potential functions. The fit is characterized by a maximum absolute error equal to 0.69 microEh and a mean error equal to -0.018 microEh.