Investigation of Multiple-Bond Dissociation Using Brillouin-Wigner Perturbation with Improved Virtual Orbitals

An improved virtual orbital complete active space configuration interaction reference function-based multireference Brillouin-Wigner perturbation approach (IVO-BWMRPT) that avoids the numerical divergence because of the intruder problem by focusing on obtaining a single root of the many-body Hamiltonian is used to compute dissociation energy surfaces and spectroscopic constants of C₂, N₂, and CN radicals. For such correlated molecules, the computational demand to delineate the wavefunction exactly is quite challenging. The IVO-BWMRPT method, a convenient and effective way to handle quasidegenerate situations, accurately captures different correlations and is capable of treating the variation of multiconfigurational nature of wave functions that occur during the multiple-bond breaking processes. Spectroscopic constants extracted from the computed surface are in good agreement with experimental or benchmark results, indicating that the components of the IVO-BWMRPT scheme must perform in harmony for providing a well-behaved and consistent description of all computed bond lengths.