  The multiconfiguration Dirac-Hartree-Fock method is applied to study the
electron affinities of At and its homologous elements Cl, Br, and I. Our method
of calculation is validated through the comparison with the available
experimental electron affinities of Cl, Br, I, and other theoretical values.
The agreement between our predicted electron affinities and the available
experimental values for Cl, Br, and I is within 0.2%, which is an improvement
of more than a factor of 10 over previous theoretical studies. Applying the
same method to At, the electron affinity of At is predicted to be 2.3729(46)
eV.
