Bross David H, Peterson Kirk A
Department of Chemistry, Washington State University, Pullman, Washington 99164-4630, USA.
J Chem Phys. 2015 Nov 14;143(18):184313. doi: 10.1063/1.4935492.
Spectroscopic constants (Te, re, B0, ωe, and ωexe) have been calculated for the low-lying electronic states of UF, UF(+), UCl, and UCl(+) using complete active space 2nd-order perturbation theory (CASPT2), with a series of correlation consistent basis sets. The latter included those based on both pseudopotential (PP) and all-electron Douglas-Kroll-Hess Hamiltonians for the U atom. Spin orbit (SO) effects were included a posteriori using the state interacting method using both PP and Breit Pauli (BP) operators, as well as from exact two-component methods for U(+) and UF(+). Complete basis set (CBS) limits were obtained by extrapolation where possible and the PP and BP calculations were compared at their respective CBS limits. The PP-based method was shown to be reliable in calculating spectroscopic constants, in particular when using the state interacting method with CASPT2 energies (SO-CASPT2). The two component calculations were limited by computational resources and could not include electron correlation from the nominally closed shell 6s and 6p orbitals of U. UF and UCl were both calculated to have Ω = 9/2 ground states. The first excited state of UCl was calculated to be an Ω = 7/2 state at 78 cm(-1) as opposed to the same state at 435 cm(-1) in UF, and the other low-lying states of UCl showed a similar compression relative to UF. Likewise, UF(+) and UCl(+) both have Ω = 4 ground states and the manifold of low-lying excited Ω = 3, 2, 1, 0 states was energetically closer together in UCl(+) than in UF(+), ranging up to 776 cm(-1) in UF(+) and only 438 cm(-1) in UCl(+). As in previous studies, the final PP-based SO-CASPT2 results for UF(+) and UF agree well with experiment and are expected to be predictive for UCl and UCl(+), which are reported here for the first time.
使用完全活性空间二阶微扰理论（CASPT2）和一系列相关一致基组，计算了UF、UF(+)、UCl和UCl(+)低电子态的光谱常数（Te、re、B0、ωe和ωexe）。后者包括基于赝势（PP）和U原子的全电子Douglas-Kroll-Hess哈密顿量的基组。自旋轨道（SO）效应通过使用PP和Breit Pauli（BP）算符的态相互作用方法事后纳入，以及通过U(+)和UF(+)的精确二分量方法纳入。在可能的情况下通过外推获得完全基组（CBS）极限，并在各自的CBS极限下比较PP和BP计算。结果表明，基于PP的方法在计算光谱常数时是可靠的，特别是在将态相互作用方法与CASPT2能量（SO-CASPT2）一起使用时。二分量计算受到计算资源的限制，无法包括U的名义上闭壳层6s和6p轨道的电子关联。计算得出UF和UCl均具有Ω = 9/2基态。UCl的第一激发态计算为Ω = 7/2态，能量为78 cm(-1)，而在UF中该态为435 cm(-1)，UCl的其他低电子态相对于UF表现出类似的压缩。同样，UF(+)和UCl(+)均具有Ω = 4基态，UCl(+)中低激发的Ω = 3、2、1、0态的多重态在能量上比UF(+)中的更接近，UF(+)中高达776 cm(-1)，而UCl(+)中仅为438 cm(-1)。与之前的研究一样，基于PP的UF(+)和UF的最终SO-CASPT2结果与实验结果吻合良好，预计对UCl和UCl(+)具有预测性，本文首次报道了它们的结果。
