Structure and energetics for an additional H absorbed into superionic phase of CsHSO₄ by a first-principles study

Using first-principles methods, we have studied the crystal structure of the CsHSO₄ superionic phase, and the stability for an additional H absorbed in CsHSO₄ in various charged states. The charged states were calculated by using neutral, negatively charged (-), and positively charged (+) supercells. For a perfect crystal, the structure in which all protons occupy the 16f-sites is found to be more stable than that in which protons occupy the 8e-sites. Concerning the stability of an additional H in CsHSO₄, we found the SO₄ tetrahedron is broken when the supercell is optimized in either the neutral or the negatively charged state. The calculated formation energy for an additional neutral H in CsHSO₄ indicates that this H can not be absorbed into CsHSO₄. In the positively charged state, the calculated formation energy indicates that many additional protons may be absorbed into CsHSO₄ to form a high chemical potential on one side.