用Gaussian98程序计算钪和钛原子价层电子组态能量

Calculations of electronic configuration energies of scandium and titanium by Gaussian 98

用Gaussian 98程序计算了钪和钛原子的价电子组态能量 .计算表明 ,Hartree -Fock(HF)迭代应采用可靠性较高的QC标准方法 ,所得的波函数要进行稳定性分析 ,根据布居分析调整电子的初始占据轨道 ,以便最终得到所需要的原子组态 .在全组态相互作用CASSCF计算中 ,需要用关键词GUESS =ALTER选择适当的活动组态空间 .计算结果说明 ,随着计算从基态转向激发态、从原子序数小的钪转向原子序数大的钛 ,需要考虑的因素明显加多 .根据HF ,QCISD(T)和PM4SDTQ计算得到Sc∶3d2 4s(4F)与Sc∶3d4s2 (2 D)的能量差分别是 96 .80 ,15 2 .92和 14 9.10kJ/mol,与实验值 138.75kJ/mol相一致 .根据HF ,QCISD (T)和CASSCF(4,5 )计算得到Ti∶3d3 4s(5F)和Ti∶3d2 4s2(3 F)的能量差分别为 5 7.85 ,91.74和 82 .0 6kJ/mol,与实验值 80 .

Electronic configuration energies of scandium and titanium have been calculated at 6-311+G(3 df )level by Gaussian 98 program,using Hartree-Fock calculation(HF),full fourth-order mller-plesset perturbation theory with single,double,triple and quadruple substitutions(PM4 SDTQ),quadratic configuration interaction technique including single and double substitutions with a triples contribution to the energy added,or complete active space multiconfiguration SCF(CASSCF)with 4 electrons and 5 orbitals.The results show that the calculations of electronic configuration energies by Gaussian 98 are not a black box for transition metal atoms,especially for excited states.Designing and completing these calculations successfully require considerable care and patience.In the HF calculation,it is noted that the stability of the HF wavefunction must be tested in each calculation,and that electron population analysis must be carried out to check if the obtained energy is corresponding to the desired electronic configuration of an atom.The quadratically convergent SCF procedure(QC),but not the default method[Pulay's Direct Inversion in the Iterative Subspace extrapolation method(DIIS)]in Gaussian 98,gives a stable HF wavefunction corresponding to Sc∶ 3d4s 2( 2D) .In order to obtain the stable states corresponding to the excite state of Sc∶ 3d 24s( 4F) and the ground state of Ti,the keyword,'STABLE=OPT',must be added.To obtain the stable state corresponding to the excited state of the heavier atom of Ti∶ 3d 34s( 5F) ,a wise initial guess of the occupied orbitals is also indispensable in addition to the