Kinetic peaks and step in the KS potential for molecular dissociation

Sharp features, such as peaks and steps, are known to arise in the KS potential to describe molecular dissociation [1] and can be traced back to well-defined components of the total KS potential, the so-called (correlation) kinetic and response ones.

We consider a two-electron, 1D model of a dissociating heteronuclear molecule and construct these components individually, showing the appearance of a secondary kinetic peak located where the step structure of the response potential goes to zero, as theorised in reference [2]. Furthermore, we calculate the kinetic and response potentials for a dissociating homonuclear dimer subject to a linear electric field: the secondary peak is observed also in this case, supporting our intuition that a homonuclear molecule subject to a field is polarized and acts “as if” heteronuclear.

The presence of a peak of relatively sizeable intensity (10^-2/ 10^-3) in drastically low-density regions (below 10^-50 in some cases) highlights the extreme sensitivity of the exact KS potential and the difficulty of designing density functional approximations to tackle dissociation processes.

[1] O. V. Gritsenko and E. J. Baerends, Phys. Rev. A 54, 1957 (1996). 

[2] S. Giarrusso, S. Vuckovic, and P. Gori-Giorgi, J. Chem. Theory Comput. 14, 4151 (2018)