Heavy Element Effects in the Diagonal Born–Oppenheimer Correction within a Relativistic Spin-Free Hamiltonian

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• 作者：Yuji Imafuku ; Minori Abe ; Michael W. Schmidt ; Masahiko Hada
• 刊名：Journal of Physical Chemistry A
• 出版年：2016
• 出版时间：April 7, 2016
• 年：2016
• 卷：120
• 期：13
• 页码：2150-2159
• 全文大小：466K
• ISSN：1520-5215

文摘

Methodologies beyond the Born–Oppenheimer (BO) approximation are nowadays important to explain high precision spectroscopic measurements. Most previous evaluations of the BO correction are, however, focused on light-element molecules and based on a nonrelativistic Hamiltonian, so no information about the BO approximation (BOA) breakdown in heavy-element molecules is available. The present work is the first to investigate the BOA breakdown for the entire periodic table, by considering scalar relativistic effects in the Diagonal BO correction (DBOC). In closed shell atoms, the relativistic E_DBOC scales as Z^1.25 and the nonrelativistic E_DBOC scales as Z^1.17, where Z is the atomic number. Hence, we found that E_DBOC becomes larger in heavy element atoms and molecules, and the relativistic E_DBOC increases faster than nonrelativistic E_DBOC. We have further investigated the DBOC effects on properties such as potential energy curves, spectroscopic parameters, and various energetic properties. The DBOC effects for these properties are mostly affected by the lightest atom in the molecule. Hence, in X₂ or XAt molecule (X = H, Li, Na, K, Rb, and Cs) the effect of DBOC systematically decreases when X becomes heavier but in HX molecules, the effect of DBOC seems relatively similar among all the molecules.