Ab initio calculations of small hydrides including electron correlation

Five different structures of CH₅⁺ and one structure of CH₅^– are calculated using a gaussian basis both in the SCF approximation and with the inclusion of electron correlation in the independent electron pair approximation (IEPA). While on SCF level the C_sstructure of CH₅⁺ has to lowest energy, the energy difference between the C_sand C_2vstructures becomes negligible if correlation is included. In contrast to this the approach of a proton to CH₄ at large and intermediate distances is most favorable towards a corner of the CH₄ tetrahedron which means a structure. The decomposition of CH₅⁺ into CH₃⁺ and H₂ requires 20kcal/mol on SCF level and 40 kcal/mol if correlation is included.