Isotope shift in the electron affinity of lithium

Abstract

Very accurate electron affinity ͑EA͒ calculations of 6 Li and 7 Li ͑and ϱ Li͒ have been performed using explicitly correlated Gaussian functions and a variational approach that explicitly includes the nuclear motion in the calculations ͑i.e., the approach that does not assume the Born-Oppenheimer approximation͒. The leading relativistic and quantum electrodynamics corrections to the electron affinities were also calculated. The results are the most accurate theoretical values obtained for the studied systems to date. Our best estimates of the 7 Li and 6 Li EAs are 4984.9842͑30͒ and 4984.9015͑30͒ cm −1 , respectively, and of the 7 Li / 6 Li EA isotope shift is 0.0827 cm −1 .

Lower Rydberg2Dstates of the lithium atom: Finite-nuclear-mass calculations with explicitly correlated Gaussian functions

“…It shows the convergence of the total energies of the 7 Li states with the number of basis functions. In the table, we also show the energies of 6 Li and ∞ Li calculated with 4000 ECGs, that is, the largest basis sets used in the calculations.…”

“…The optimization of the ECG basis sets for these states have been performed for the 7 Li isotope and then used to also calculate the 2 D energy levels of the 6 Li isotope, as well as of the lithium atom with an infinite nuclear mass ( ∞ Li). The ∞ Li are shown because they can be compared with the results obtained in the standard way that involves the BO approximation.…”

“…Very accurate results for three-, four-, and five-electron atoms (with all electrons in s states or one electron in a p state and the rest in s states) have been obtained with those functions [6][7][8][9][10][11][12][13]. The main advantage of using Gaussians in atomic calculations is due to the simplicity of the Hamiltonian and overlap integrals with those functions, which can be evaluated analytically in a compact form for an arbitrary number of electrons.…”

“…These deficiencies cause a certain slowdown of the convergence to the exact nonrelativistic wave function. Fortunately, as the calculations have shown [6][7][8][9][10][11][12][13], they can be effectively remedied by using longer expansions and by performing extensive optimization of the Gaussian nonlinear parameters using the variational energy minimization.…”

“…was obtained). We also calculated the energy of the lowest 2 D state of 7 Li, as well as the energy of the second-lowest state, using the finite-nuclear-mass approach. The calculation was an example included in the work [3] that featured implementation of the ECG variational method for calculating D states of small atomic systems.…”