We perform a systematic investigation of the electronic properties of the 2 Σ + ground state of Lialkaline-earth dimers. These molecules are proposed as possible candidates for quantum simulation of lattice-spin models. We apply powerful quantum chemistry coupled-cluster method and large basis sets to calculate potential energies and permanent dipole moments for the LiBe, LiMg, LiCa, LiSr, and LiYb molecules. Agreement of calculated molecular constants with existing experimental data is better than or equal to 8%. Our results reveal a surprising irregularity in the dissociation energy and bond length with an increase in the reduced mass of the molecule. At the same time the permanent dipole moment at the equilibrium separation has the smallest value between 0.01 a.u. and 0.1 a.u. for the heaviest (LiSr and LiYb) molecules and increases to 1.4 a.u. for the lightest (LiBe), where 1 a.u. is one atomic unit of dipole moment. We consider our study of the 2 Σ + molecules a first step towards a comprehensive analysis of their interactions in an optical trap.

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We compute the wavelengths and oscillator strengths for the 3s, 3d → 2p, and 3p → 2s emission lines in Fe xix and Fe xx ions by using a configuration interaction Dirac-Fock and Dirac-Fock-Sturm method combined with second-order Brillouin-Wigner perturbation theory. We provide a complete list of computed wavelengths and oscillator strengths in both the velocity and length gauge for these transitions, many of which have never previously been reported. A comparison of our data with laboratory measurements and other theoretical predictions allows us to estimate an uncertainty of ∼2 mÅ in the wavelengths and an uncertainty of 2%-3% in the oscillator strengths. We expect that our calculations will provide a means of identifying emission lines from astrophysical sources and improve the ability to detect blending in X-ray grating spectra from Chandra and XMM-Newton. As an example, we present a simulated emission spectrum of Capella and find improved agreement between the observations and our calculations, compared with previous data sets.

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