Connection between a few Jeziorski‐Monkhorst ansatz‐based methods

Different Jeziorski‐Monkhorst ansatz‐based methods are unified according to how to group terms to eliminate the redundancy problem. It is found that some seemingly different methods used to do MRCC are equivalent. It is argued that the various defining equations are not entirely proper, in the sense that the proper residual condition is not satisfied. This may partially rationalize the unsatisfactory performance of the various methods for single reference systems. In contrast, the MRexpT method satisfies the proper residual condition and it is expected that it will outperform other JM ansatz‐based methods in single‐reference cases.