Ground state of plutonium dioxide in electric fields ranging from-0.005 to 0.005 a.u. are optimized using density functional theory DFr/B3LYP with SDD for Pu and 6-311 + G^* for O. Excitation energies in electric fields are calculated with time-dependent DFT method. It is shown that electronic state, total energy, molecular geometry, dipole moment and excitation energy are strongly dependent on the strength of applied electric field. Dependence of excitation energies on applied electric field strength agrees approximately with that proposed by Grozema. Spectra of the first five excited states are in the region of visible-infrared-far infrared with wavelength ranging from 501.47 to 10 291.5nm.

The energies, equilibrium geometries and harmonic frequencies of X¹∑_g⁺, A¹∑_u⁺ and B¹Ⅱ_u, of molecule Na₂ are calculated by the GSUM (Group Sum of Operators) method of SAC/SAC-CI using basis sets 6-311 ++ g, 6-311g^** and cc-PVTZ. It is found that 6-311g^** is suitable for energy calculation of molecule Na₂. The potential curves of ground states and excited states are scanned by the SAC/6-311g^** and SAC-CI/6-311g^** methods, respectively. A least square is fitted to a Murrell-Sorbie function.The spectroscopy constants (B_e, α_e, ω_e, and ω_eX_e) are calculated and show good agreement with experiment. It is believed that Murrell-Sorbie function and the SAC/SAC-CI method are suitable for ground states and for low-lying excited states as well.