An Analytical Approach to Predict High-spin Stability of Conjugated Hydrocarbon Radical Polymers using Minimized Mixing Nonbonding Molecular Orbitals

A method of analytical prediction (AP) and the corresponding index LAP used for predicting high-spin stability of alternant conjugated hydrocarbon radical polymers were generalized for both non-disjoint closed-type and open-type systems. The general formulas of LAP were derived analytically as the function of the number of unpaired electrons, denoted as N, without performing any localization procedure to attain the minimum mixing between nonbonding molecular orbitals (NBMOs). To examine the reliability of this analytical treatment, the relationship between the LAP and the energy stability in high-spin state was investigated by ab initio method for open-shell systems. It was shown that this approach can be a useful tool for qualitative prediction of ferromagnetism in alternant conjugated hydrocarbon radical polymers.