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arXiv physics/9902019physics.chem-phphysics.atm-clus
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Be_2分子的基态光谱常数的再研究

The ground-state spectroscopic constants of Be_2 revisited

Jan M. L. Martin

摘要:

广泛的从头算校准计算结合外推到无限基极限导致的基态的离解能Be_2,D_e=944 \pm 25 1/cm,大大高于公认的实验值,并证实了最近的理论研究结果.我们最好的计算光谱观测值(expt。参数值)为G(1)-G(0)=223.7(223.8),G(2)-G(1)=173.8(169 \pm 3),G(3)-G(2)=125.4(122 \pm 3),B_0=0.6086(0.609)1/cm;基于全原子价CAS(4/8)参考的多参考计算受到角度相关的不平衡描述的影响;为了最大的准确性,需要包括$(3s,3p)$轨道的CAS(4/16)参考,而对于不太准确的工作,建议使用CAS(4/4)参考。计算耦合集群结果的质量关键取决于连接的三重激励的描述; CC 5SD(T)方法由于误差补偿而产生异常好的结果。

英文摘要:

Extensive ab initio calibration calculations combined with extrapolations towards the infinite-basis limit lead to a ground-state dissociation energy of Be_2, D_e=944 \pm 25 1/cm, substantially higher than the accepted experimental value, and confirming recent theoretical findings. Our best computed spectroscopic observables (expt. values in parameters) are G(1)-G(0)=223.7 (223.8), G(2)-G(1)=173.8 (169 \pm 3), G(3)-G(2)=125.4 (122 \pm 3), and B_0=0.6086 (0.609) 1/cm; revised spectroscopic constants are proposed. Multireference calculations based on a full valence CAS(4/8) reference suffer from an unbalanced description of angular correlation; for the utmost accuracy, a CAS(4/16) reference including the $(3s,3p)$ orbitals is required, while for less accurate work a CAS(4/4) reference is recommended. The quality of computed coupled cluster results depends crucially on the description of connected triple excitations; the CC5SD(T) method yields unusually good results because of an error compensation.

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