Precise theoretical calculation of the nuclear matrix elements (NME) and phase space factors
(PSFs) are essential for predicting and interpreting data in double beta decay (DBD) experiments.
In particular, from PSFs one can derive predictions of the electron energy spectra and angular
correlations that can be used for detector calibration, background characterization, and differen
tiation between double beta decay modes. In this work, we provide updated values of PSFs for
the (2𝜈𝛽−𝛽−) mode for transitions from ground states to ground and excited 0+ and 2+ states, for
a large number of isotopes. The calculations are performed with an adapted Dirac-Hartree-Fock
Slater method, which allows accurate treatment of the electron wave functions and includes key
atomic features like screening, finite nuclear size, exchange corrections, and phase shift effects.