Intense electron correlation dependence of the first hyperpolarizabilities β of a nitroxide radical and formaldehyde

The static first hyperpolarizability (β) of a small-sized open-shell system including a nitroxide radical, H2NO, is studied using ab initio molecular orbital and density functional methods. The static β of H2CO is also evaluated as a reference closed-shell system. Intense electron correlation dependence of β for H2NO and H2CO is observed. Their tendencies are analyzed from the viewpoint of spatial contributions of electrons to β by using plots of hyperpolarizability densities.