We present recent high accuracy ab initio calculations of electronic potential energy surfaces and non-adiabatic couplings for negatively and positively charged diatomic ions relevant to edge plasma processes and plasma cooling in thermonuclear fusion. In particular, the multi-reference single- and double- configuration interaction method is applied to various charge transfer collision processes involving single- and double- electron capture mediated by cationic molecular compounds. A case study of the C⁴⁺+ He →C²⁺+ He²⁺ is given. Next, we analyze the specific features of heavy neutral hydrides. Using the AgH molecule as an example, it is demonstrated that relativistic effective core potentials can be accurately used to reproduce spectroscopic measurements. Common diabatization techniques (elimination of derivative coupling vs. dipole moment diagonalization) are compared and discussed. Finally, we present the case study of the simplest molecular anion, H₂^-(²Σ_u⁺). The coupled cluster method up to tripple excitations (CCSD(T)) is applied to this prototype electronic structure system for internuclear separation large than 3 a.u. Using large augmented standard basis sets, we achieve accuracy of 0.1 mE_h. An additional order of accuracy is obtained by applying the complete basis set extrapolation method. The poster focuses both on ab initio calculations of the electronic states [1,2] and applications in edge plasma processes [3,4].

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