二氢化钚分子激发态结构的外场效应

The effect of external electric field on the excited states of plutonium dihydride

采用密度泛函(DFT)方法B3LYP/Gen,在Pu为SDD基组、H为6-311++G**基组水平上优化得到了分子轴方向不同电偶极场(-0·005—0·005a.u.)作用下,二氢化钚的基态电子状态、几何结构、电偶极矩和分子总能量.在优化构型下用同样的基组采用含时密度泛函(TDDFT)方法(TD-B3LYP)研究了同样外电场条件下对二氢化钚的激发能和振子强度的影响.计算结果表明,分子几何构型与电场大小和方向呈现较强的依赖,电场强度增加基态偶极矩随电场强度线性增加,H-Pu-H的角度线性减小,分子总能量线性减小;激发能随电场强度增加而减小,且对电场方向的依赖呈现近似对称性,满足Grozema关系.电场对振子强度的影响比较复杂,但仍满足跃迁选择定则.

The ground states of plutonium dihydride under electric field ranging from - 0. 005 to 0.005 a.u. have been optimized using density functional theory DFT/B3LYP with SDD for Pu and 6-311 ＋ ＋ G^＊＊ for H. The excitation energies and oscillator strengths have been calculated under the same electric field employing the time-dependent DFT method. The results show that the electronic state, total energy, molecular geometry, dipole moment and excitation energy are strongly dependent on the applied field strength. As the electric field changes from - 0.005 to 0.005 a. u., the bond length of Pu-H increases whereas the bond angle of H-Pu-H decreases because of the charge transfer induced by the applied electric field. The dipole moment of the ground state increases linearly with the applied field strength. The total energy of the ground state decreases linearly with the applied field strength. The dependence of the calculated excitation energies on the applied electric field strength fits well to the relationship proposed by Grozema. The excitation energies of the first five excited states of plutonium dihydride decrease as the applied electric field increases because the energy gap between the HOMO and LUMO become narrower with the field, which shows that the molecule is apt to be excited under electric field and hence can be easily dissociated.