Constrained-pairing mean-field theory. II. Exact treatment of dissociations to nondegenerate orbitals

Our recently proposed constrained-pairing mean-field theory (CPMFT) is here extended to deal with dissociation of electron pairs to nondegenerate orbitals. To achieve this goal, we introduce the concept of asymptotic constraints. This extended CPMFT model can exactly dissociate polyatomic molecules to restricted open-shell atoms or fragments. We present benchmarks showing how CPMFT accounts for static correlation in an accurate yet computationally inexpensive mean-field manner, while preserving space and spin symmetries. The key element of our approach is the admittance of electron number fluctuations into the wave function. (C) 2009 American Institute of Physics. [doi:10.1063/1.3257965]