title: Frequency-dependent polarizability of helium including relativistic effects with nuclear recoil terms.
abstract: Future metrology standards will be partly based on physical quantities computed from first principles rather than measured. In particular, a new pressure standard can be established if the dynamic polarizability of helium can be determined from theory with an uncertainty smaller than 0.2 ppm. We present calculations of the frequency-dependent part of this quantity including relativistic effects with full account of leading nuclear recoil terms and using highly optimized explicitly correlated basis sets. A particular emphasis is put on uncertainty estimates. At the He-Ne laser wavelength of 632.9908 nm, the computed polarizability value of 1.39181141 a.u. has uncertainty of 0.1 ppm that is 2 orders of magnitude smaller than those of the most accurate polarizability measurements. We also obtained an accurate expansion of the helium refractive index in powers of density.
authors.affiliation: Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716, USA.
authors.forename: Konrad
authors.initials: K
authors.lastname: Piszczatowski
authors.affiliation: Faculty of Chemistry, Adam Mickiewicz University, Umultowska 89B, 61-614 Poznań, Poland.
authors.forename: Mariusz
authors.initials: M
authors.lastname: Puchalski
authors.affiliation: Faculty of Chemistry, Adam Mickiewicz University, Umultowska 89B, 61-614 Poznań, Poland.
authors.forename: Jacek
authors.initials: J
authors.lastname: Komasa
authors.affiliation: Department of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland.
authors.forename: Bogumił
authors.initials: B
authors.lastname: Jeziorski
authors.affiliation: Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716, USA.
authors.forename: Krzysztof
authors.initials: K
authors.lastname: Szalewicz