Non-nuclear attractors in small charged lithium clusters, Limq (m = 2–5, q = ±1), with QTAIM and the Ehrenfest force partitioning

Abstract

In this investigation we explore the function and existence of the non-nuclear attractor (NNA) for a series of small charged lithium clusters Li_m^q (m = 2–5, q = ±1) using QTAIM and the Ehrenfest force F(r) partitioning schemes. The NNAs were found to be present in all of the Li_m^q (m = 2–5, q = ±1) clusters for QTAIM, in contrast none were found for F(r). We discovered that the anionic and cationic lithium dimers are limiting cases for minimal and maximal impact of the NNA related to the relative sparseness of total charge density ρ(r) distributions respectively. Evidence is found that the NNA in the anionic dimer is in the process of being annihilated by two neighboring BCPs. We provide a measure of the size of the NNA and find for Li_m^q (m = 2–5, q = ±1) that larger NNAs correlate with increased Li–Li separations. The NNA was determined to be a persistent feature by varying the Li separations for the cationic and anionic dimers. Very large Li separations failed to induce an NNA in the F(r) anionic dimer and therefore we conclude that F(r) is unable to detect NNAs. The metallicity ξ(r_b) was also used to measure the sparseness of the distribution of ρ(r) and significant metallic character, on the basis of ξ(r_b) > 1, was present for QTAIM but not for F(r), providing further evidence that F(r) cannot detect NNAs. Advantages of the use of Ehrenfest force F(r) partitioning scheme are discussed that include the design of nano-devices through tuning of the Ehrenfest potential V_F(ṙ_b) by the application of external forces such as a constant electric or strain field.