Bonding description of the Harpoon mechanism^†

† This paper is dedicated to Andreas Savin on the occasion of his 65th birthday.

Abstract

The lowest lying states of LiH have been widely used to develop and calibrate many different methods in quantum mechanics. In this paper, we show that the electron-transfer processes occurring in these two states are a difficult test for chemical bonding descriptors and can be used to assess new bonding descriptors on its ability to recognise the harpoon mechanism. To this aim, we study the bond formation mechanism in a series of diatomic molecules. In all studied electron reorganisation mechanisms, the maximal electron-transfer variation point along the bond formation path occurs when about half electron has been transferred from one atom to another. If the process takes place through a harpoon mechanism, this point of the reaction path coincides with the avoided crossing. The electron sharing indices and one-dimensional plots of the electron localisation function and the Laplacian of the electron density along the molecular axis can be used to monitor the bond formation in diatomics and provide a distinction between the harpoon mechanism and a regular electron reorganisation process.

GRAPHICAL ABSTRACT

Keywords:

• Chemical bonding
• harpoon mechanism
• excited states
• ionic bond
• QTAIM

Acknowledgements

The authors thank Prof. Bernard Silvi for providing reference [8].

Supplemental data for this article can be accessed at http://dx.doi.org/10.1080/00268976.2015.1121297

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes

† This paper is dedicated to Andreas Savin on the occasion of his 65th birthday.

1. Setting the position of the peaks’ separation is not exempt of numerical error. We have set the peaks’ separation after 2.5Å by neglecting values of the Laplacian below 10⁻⁴.

2. Please notice that these quantities are not size extensive and, therefore, their values can not be compared with the sum of the isolated fragments.

3. The only exception are Hilbert space partitions (such as Mulliken's or Löwdin's), which show spurious results if the calculations involve a many-body wave function and its exact pair density function [52].

Additional information

Funding

This research has been funded by the MINECO projects CTQ2014-52525-P and CTQ2014-54306-P, the Basque Country Consolidated Group Project No. IT588-13, the FEDER grant UNGI10-4E-801 (European Fund for Regional Development), the Generalitat de Catalunya (project number 2014SGR931, Xarxa de Referència en Química Teòrica i Computacional, and ICREA 2014 prize to M.S.) and the predoctoral fellowship FPU13/00176. Excellent service by the Centre de Serveis Científics i Acadèmics de Catalunya (CESCA) and technical and human support provided by SGI/IZO-SGIker UPV/EHU are gratefully acknowledged.