Comprehensive investigations on the structural modifications of negative hydrogen ion within an impenetrable spherical domain has been performed in the framework of Ritz variational method. Electron correlation plays a major role in the formation of H– ion. The Hylleraas‐type basis set expansion of wave function considered here incorporates the effect of electron correlation in an explicit manner. Energy values of 1s2 (1normalSnormale), 2p2 (3normalPnormale) and 1sn p (1,3normalPnormalo) states (n=2−5) of H– ion within confined domain have been calculated. Although the singly excited states do not exist for a “free” H– ion, well converged energy values of such states have been found within a wide range of confinement radius. The thermodynamic pressure felt by the ion inside the sphere is also estimated. The general trend shows successive destabilization of the excited energy levels with increase of pressure. The contribution of angular correlation in the energy values have been estimated. Evolution of 1s2 (1normalSnormale) and 2p2 (3normalPnormale) energy levels of H– ion as quasi‐bound states are being reported.

The Rayleigh-Ritz variational technique with a Hylleraas basis set is being tested for the first time to estimate the structural modifications of a lithium atom embedded in a weakly coupled plasma environment. The Debye-Huckel potential is used to mimic the weakly coupled plasma environment. The wave functions for both the helium-like lithium ion and the lithium atom are expanded in the explicitly correlated Hylleraas type basis set which fully takes care of the electron-electron correlation effect. Due to the continuum lowering under plasma environment, the ionization potential of the system gradually decreases leading to the destabilization of the atom. The excited states destabilize at a lower value of the plasma density. The estimated ionization potential agrees fairly well with the few available theoretical estimates. The variation of one and two particle moments, dielectric susceptibility and magnetic shielding constant, with respect to plasma density is also been discussed in detail.

The ground state energy eigenvalues of the spatially confined symmetric three-body exotic ions P s − and H + 2 have been determined under the framework of Rayleigh-Ritz variational method. The spatial confinement is simulated by considering an impenetrable spherical box of varying radius around the ion. The electron-electron correlation in P s − and the proton-proton correlation in H + 2 are properly taken care of by expanding the trial wavefunction in explicitly correlated Hylleraas type basis set. The critical radius and the corresponding critical pressure, at which the respective ions destabilize are also reported.

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