Studies on m-benzyne and phenol via improved virtual orbital-complete active space configuration interaction (IVO-CASCI) analytical gradient method

Improved virtual orbital-complete active space configuration interaction (IVO-CASCI) analytical gradient theory has been used to investigate geometrical parameters, vibrational frequencies and excitation energies of m-benzyne and phenol using different reference spaces and basis sets. Compared to the results obtained via CASSCF treatments, it has been found that the IVO-CASCI gradient method provides very satisfactory results with low computational cost. IVO-CASCI values compare reasonably well with the earlier established theoretical results and experimental values whenever available.