Relativistic and quantum electrodynamic contributions have been used, as well as improved accuracy adiabatic ones, to compute several physical effects in the helium pair potential. These effects include couplings of the electronic and nuclear motions, contributions due to Einstein’s special relativity, and the quantum electrodynamics contributions due to the interaction of the electrons with the electromagnetic field.

The computed dissociation energy and the average distance, R, for the ⁴He₂ bound state are 1.62±0.03 mK and 47.1±0.5 Å, respectively.

Krzysztof Szalewicz, University of Delaware, USA, led the study, and will now use the values computed from this potential to calibrate apparatus for measuring properties such as viscosities or the speed of sound.

• Relativistic and Quantum Electrodynamics Effects in the Helium Pair Potential
  M. Przybytek, W. Cencek, J. Komasa, G. Łach, B. Jeziorski, K. Szalewicz,
  Phys. Rev. Lett. 2010, 104, 183003.
  DOI: 10.1103/PhysRevLett.104.183003