Family of modified-contracted Schrödinger equations

This is the authors' abstract. We don't add key points for this paper.

A family of equations that combines contracted Schr\"odinger equations of different orders is reported here. Attention is focussed on the resulting second order, third order, and fourth order of these modified-contracted Schr\"odinger equations. Some of these equations are self-contained and have as fixed points those corresponding to the full-configuration interaction eigenstates. The indeterminacy, which hindered initially the use of the contracted Schr\"odinger equations, does not formally exist in these equations. Relations linking the lower-order reduced density matrices with the higher-order matrices are exactly incorporated into the modified-contracted Schr\"odinger-equations structure. The cancellation of high-order correlation terms, which is hidden in the contracted Schr\"odinger equations, now takes an explicit form.