Potential energy curves and dipole moments of five bound states are computed by high-level multi-reference configuration interaction method with all-electron aug-cc-pwCV5Z+DK for Mg atom and aug-cc-pV5Z-PP for I atom. To obtain high precise spectroscopic properties, Davidson modification, core valence correlation and relativistic correction are introduced. Based on PECs of 5 bound states, accurate spectroscopic constants, vibration levels and molecular constants of bound states are obtained by solving radial Schrödinger equation. Compared with recent theoretical calculation our results are closer to experimental datum. It shows that high precision calculation method and correlation correction are necessary for analysis of spectral properties. It provides support for further research on spectroscopic and transition characters of higher excited states of MgI molecule.

With density functional B3P86 method and cc-PV5Z base,bond lengths,dipole moments,vibration frequencies and other physical parameters of BH molecule in external electric fields are obtained.With analysis of physical parameter,scope of dissociation field is determined,appropriate parameters to scan single point energies are set,and potential energy curves are obtained.It shows physical parameters and potential energies in external electric fields,especially in reverse electric fields.Potential energy function without electric field is fitted by Morse potential.Fitting parameters are in good agreement with experiment.Potential energy under external electric fields is fitted using a potential model,which is constructed with dipole approximation.Critical electric parameters are calculated.They are consistent with other numerical results,so the model is reliable and accurate.It provides theoretical reference for molecular spectroscopy,dynamics and cooling with Stark effect.

Geometrical structures of³² S¹⁶0₂ and³⁴ S¹⁶O₂ are optimized at B3P86/cc-PV5Z level using Gaussian03 program. Equilibrium geometry。vibrational and rotational constants etc.are obtained.Total internal partition functions(TIPF)of³² S¹⁶0₂ and³⁴ S¹⁶O₂ are calculated from 70 to 6000K Witll product approximation.Rotational partition sums adopt WATSON rigidmtator model and vibrational partition sums use harmonie oscillator approximation.It is found that calculated results are consistent with those offered by HITRAN database.and errors show linear correlation approximately from 70 to 3000 K.By fitting errors,TIPF were corrected at high temperatures range from 3000 to 6000 K.Corrected values are fitted to a four-order polynomial of T.and coefficients are evaluated. This allows a rapid and accurate calculation of TIPF at 3 000-6 000 K.

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.