Theoretical studies on hyperpolarizabilities of nitroxide species. I

Static third-order hyperpolarizabilities γ of some open-shell systems including nitroxide radical sites are investigated by ab initio MO method. The dependences of basis sets and electron correlation effects on γ values for H2NO, H2CO, (CH3)2NO and (CH3)2CO are examined. It is found that Møller-Plesset second-order perturbation (MP2) method using the extended basis set with diffuse p and d functions can provide reasonable descriptions of relative tendencies of γ for H2NO, H2CO and (CH3)2CO, while higher-order correlation effects at the CCSD(T) level are crucial for qualitative descriptions of γ of (CH3)2NO.