Manipulative Effects Of Spin Multiplicity And Excess Electron Number On Nonlinear Optical Response

In present work, using the density functional with medium rangeelectron correlation M06-2X method, we obtain seven new linear/cyclicstructures of electride molecules with different excess electron numbers(n=1,2, and3). The novel effects of the spin multiplicity and the excesselectron number on the structure and static first hyperpolarizability (β0)are revealed for new electride molecules with multiexcess electrons.(1) For the spin effect on molecular structure, the low spinmultiplicity (ground state) of linear structures (1L2and2L3) brings about ashort Na···Na distance indicating the formation of an extraordinaryNa Na bond, which bends the linear molecular structure. Notably, anextraordinary Na Na single bond between two doped Na atoms is aspecial Na Na bent σ single bond including the bent bridge of the excesselectron pair and two bridgehead Na+cations for the first time. Here, theelectronic structure of the Na Na unit can be interestingly described as Na+(e2)2Na+.(2) For the NLO response, the low spin multiplicity brings a verylarge β0value, for instance, the considerable β0of22.7×104au for2L3with the low spin multiplicity is larger by about21times than that of1.1×104au for4L3with the high spin multiplicity due to the spin reversal ofonly one excess electron. It shows that the spin multiplicity effect on thefirst hyperpolarizability is remarkable.(3) For the effect of excess electron number, it is shown that the β0value increases rapidly with increasing excess electron number.(4) For the molecular shape effect on β0, the circular structuredramatically reduces the β0value for the low spin states but obviouslyenhances the β0value for the high spin states.On the basis of effects of the spin multiplicity and the excess electronnumber as well as the molecular shape on the static firsthyperpolarizability, a novel molecular manipulation strategy of enhancingthe NLO response is found. That is, a long chain-shaped electridemolecule (for instance,2L3) with multiexcess electrons in the low spinstate may bring a considerable static first hyperpolarizability. Besidestraditional structural influencing factors, this work will also enlighten anew electronic perspective on a new NLO molecule investigationincluding the manipulations of spin multiplicity and excess electronnumber for electride molecules.