Nonnuclear Attractors in Heteronuclear Diatomic Systems

Abstract

Nonnuclear attractors (NNAs) are observed in the electron density of a variety of systems, but the factors governing their appearance and their contribution to the system's properties remain a mystery. The NNA occurring in homo- and heteronuclear diatomics of main group elements with atomic numbers up to Z = 38 is investigated computationally (at the UCCSD/cc-pVQZ level of theory) by varying internuclear separations. This was done to determine the NNA occurrence window along with the evolution of the respective pseudoatomic basin properties. Two distinct categories of NNAs were detected in the data analyzed by means of catastrophe theory. Type "a" implies electronic charge transfer between atoms mediated by a pseudoatom. Type "b" shows an initial relocation of some electronic charge to a pseudoatom, which posteriorly returns to the same atom that donated this charge in the first place. A small difference of polarizability between the atoms that compose these heteronuclear diatomics seems to favor NNA formation. We also show that the NNA arising tends to result in some perceptible effects on molecular dipole and/or quadrupole moment curves against internuclear distance. Finally, successive cationic ionization results in the fast disappearance of the NNA in Li2 indicating that its formation is mainly governed by the field generated by the quantum mechanical electronic density and only depends parametrically on the bare nuclear field/potential at a given molecular geometry.

Molecular QTAIM Topology Is Sensitive to Relativistic Corrections

“…Inside every basin there is exactly one local maximum in the electron density, which is typically at the location of an atomic nucleus, although nonnuclear attractors also occasionally exist . Local maxima in the electron density are called attractors.…”

“…[22,26] Inside every basin there is exactly one local maximum in the electron density,w hich is typicallya tt he location of an atomic nucleus, although nonnuclear attractors also occasionally exist. [32][33][34] Local maxima in the electron density are called attractors.B etween two basins that share ab oundary surface, there is always ab ond critical point (BCP). This is the minimum density point along the ridgeline( called abond path) that connects the two attractors and the maximum density point on the bounding surface between the basins.…”

Highs and Lows of Bond Lengths: Is There Any Limit?

“…The confirmation of this mechanical‐electronic correlation cannot be extended to heteronuclear diatomic bonds since, as discussed by Pendás et al [48] . and others, [49] the occurrence of NNMs in these cases is less likely. However, the expected core effects at the r hs limit should be produced in a similar way as in homonuclear bonds.…”

Highs and Lows of Bond Lengths: Is There Any Limit?

“…Thec onfirmation of this mechanical-electronic correlation cannot be extended to heteronuclear diatomic bonds since,a sd iscussed by Pendµse tal. [48] and others, [49] the occurrence of NNMs in these cases is less likely.However, the expected core effects at the r hs limit should be produced in as imilar way as in homonuclear bonds.T hanks to the ELF, aquantitative account of this situation can be also disclosed. Taking as an example the CÀObond in ethanol, we illustrate in Figure 3h ow the ELF CÀOb ond attractor suffers ac usp catastrophe in the compressed state transforming into asaddle point and two new attractors.Furthermore,each of these new ELF basins yields 0.8 e À .T hese topological changes in the index of the ELF bond attractor and concomitant increasing of the e À populations when the CÀObond is squeezed from its 1.45 equilibrium distance to 0.8 along the bond axis,are also representative of what happens in the heteronuclear bonds of our study.Inspite of the reduced number of selected bonds and that no more exhaustive analysis were carried out with alternative descriptors (HOMO-LUMO gaps, [50] natural bond orbital electron populations, [51] the effective number of unpaired electrons, [52] etc.…”