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Interaction between LiH molecule and Li atom from state-of-the-art electronic structure calculations.

Skomorowski, Wojciech and Pawlowski, Filip and Korona, Tatiana and Moszynski, Robert and Zuchowski, Piotr S. and Hutson, Jeremy M. (2011) 'Interaction between LiH molecule and Li atom from state-of-the-art electronic structure calculations.', Journal of chemical physics., 134 (11). p. 114109.

Abstract

State-of-the-art ab initio techniques have been applied to compute the potential energy surface for the lithium atom interacting with the lithium hydride molecule in the Born–Oppenheimer approximation. The interaction potential was obtained using a combination of the explicitly correlated unrestricted coupled-cluster method with single, double, and noniterative triple excitations [UCCSD(T)-F12] for the core–core and core–valence correlation and full configuration interaction for the valence–valence correlation. The potential energy surface has a global minimum 8743 cm−1 deep if the Li–H bond length is held fixed at the monomer equilibrium distance or 8825 cm−1 deep if it is allowed to vary. In order to evaluate the performance of the conventional CCSD(T) approach, calculations were carried out using correlation-consistent polarized valence X-tuple-zeta basis sets, with X ranging from 2 to 5, and a very large set of bond functions. Using simple two-point extrapolations based on the single-power laws X−2 and X−3 for the orbital basis sets, we were able to reproduce the CCSD(T)–F12 results for the characteristic points of the potential with an error of 0.49% at worst. The contribution beyond the CCSD(T)–F12 model, obtained from full configuration interaction calculations for the valence–valence correlation, was shown to be very small, and the error bars on the potential were estimated. At linear LiH–Li geometries, the ground-state potential shows an avoided crossing with an ion-pair potential. The energy difference between the ground-state and excited-state potentials at the avoided crossing is only 94 cm−1. Using both adiabatic and diabatic pictures, we analyze the interaction between the two potential energy surfaces and its possible impact on the collisional dynamics. When the Li–H bond is allowed to vary, a seam of conical intersections appears at C2v geometries. At the linear LiH–Li geometry, the conical intersection is at a Li–H distance which is only slightly larger than the monomer equilibrium distance, but for nonlinear geometries it quickly shifts to Li–H distances that are well outside the classical turning points of the ground-state potential of LiH. This suggests that the conical intersection will have little impact on the dynamics of Li–LiH collisions at ultralow temperatures. Finally, the reaction channels for the exchange and insertion reactions are also analyzed and found to be unimportant for the dynamics.

Item Type:Article
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Status:Peer-reviewed
Publisher Web site:http://dx.doi.org/10.1063/1.3563613
Publisher statement:© 2011 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Skomorowski, Wojciech and Pawlowski, Filip and Korona, Tatiana and Moszynski, Robert and Zuchowski, Piotr S. and Hutson, Jeremy M. (2011) 'Interaction between LiH molecule and Li atom from state-of-the-art electronic structure calculations.', Journal of chemical physics., 134 (11). p. 114109 and may be found at http://dx.doi.org/10.1063/1.3563613
Date accepted:No date available
Date deposited:27 June 2013
Date of first online publication:2011
Date first made open access:No date available

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