The 1s(2) -> 1s2p(P-1) excitation energy for helium atoms in liquid helium, solid helium and helium bubbles in metals

The energy of the He 1s(2) --> 1s2p(P-1) transition for helium atoms in liq uid helium, solid helium and helium bubbles in metals is greater than for f ree helium atoms by an amount known as the energy shift. The energy shift i s calculated by combining the results of ab-initio self-consistent field el ectronic structure calculations with corrections to account for the effects of electron correlation. The corrections consist of a short-range correlat ion energy which is calculated using density functional theory and a disper sion energy which is calculated using a modified form of the van der Waals interaction. The method allows significant improvements to be made on previ ous calculations and the predicted Values of the energy shift are in good a greement with the experimental results.