Relativistic Correction from the Four-Body Nonadiabatic\nExponential Wave Function

We present a method\nfor calculating the relativistic correction\nin hydrogen molecules that significantly exceeds the accuracy of all\nthe previous literature results. This method utilizes the explicitly\ncorrelated nonadiabatic exponential wave function, and thus treats\nelectrons and nuclei equivalently. The proposed method can be applied\nto any rovibrational state, including highly excited ones. The numerical\nprecision of the relativistic correction reaches several kHz (∼10<sup>–7</sup> cm<sup>–1</sup>), which is below the best\nexperimental accuracy.