Analytical potential energy function for the electronic states X~2∑~+,A~2∏ of MgH molecule

The equilibrium geometries of two electronic states(the ground state X2∑+,the first degenerate state A2∏) of MgH molecule have been calculated using the method of Symmetry Adapted Cluster-Configuration Interaction(SAC-CI) and the Quadratic CI method including Single and Double substitutions(QCISD(T)) with the basis sets cc-PVQZ,aug-cc-PVTZ,6-311++g and 6-311++g(3df,2pd).Comparing among the above mentioned four basis sets,the conclusion is gained that the basis set 6-311++g(3df,2pd) is the most suitable for the energy calculation of MgH molecule.The whole potential curves for these electronic states are further scanned using QCISD(T)/6-311++g(3df,2pd) method for the ground state and SAC-CI/6-311++g(3df,2pd) method for the excited states.The potential energy functions and relevant spectrum constants(ωe,ωeχe,Be,αe) of these states are obtained by fitting to the Murrell-Sorbie function and the modified Murrell-Sorbie+c6 function,respectively.The results show that the spectrum constants derived from the modified Murrell-Sorbie+c6 function are in very good agreement with the experimental data,which indicate that the modified Murrell-Sorbie+c6 function can correctly present the potential energy function of the ground state and the first degenerate state of MgH molecule.