Parity violation energies of C_4 H_4 X_2 molecules for X=O, S, Se, Te and Po

Parity-violating contributions, with the same magnitude but opposite sign, to the energies of 1,2 enantiomers of dioxin, dithiin, diselenin, ditellurin, and dipolonin have been calculated. Theoretical predictions, which can be classified among the largest reported so far, indicate that the P enantiomer is energetically more stable than M. As expected, non-relativistic effects increase with the first power of the neutron number and the fourth power of the atomic number for X= O, S, Se, Te, Po. The trend predicted by Laerdahl and Schwerdtfeger [Phys. Rev. A {60}, 4439 (1999)] and by Berger [J. Chem. Phys. {129}, 154105 (2008)] for H_2X_2 molecules, characterized by free rotation about the X-X internuclear axis, is therefore confirmed for the series of more rigid C_4 H_4 X_2 compounds, in which limited deformations can take place.