Effectiveness of Symmetry and the Pauli Condition on the 1 Matrix in the Reduced-Density-Matrix Variational Principle

Application is made of the reduced-density-matrix variational principle using a pair matrix constructed of geminals obtained from $1s$, $2s$, and $2p$ orbitals. The objective is to test the strength of the Pauli restriction on the 1 matrix and certain symmetry conditions for improving the lower bound to the ground-state energy. With the particular trial pair matrix used, the Pauli restriction on the 1 matrix improves the percentage error in the energy lower bound for C⁺⁺ by a factor of approximately 6.