In this investigation, we seek to understand the role of non-nuclear attractors (NNAs) of the neutral Li-2 dimer subjected to an electric (+/- E) field that is directed parallel (+/- E-x) and perpendicular (+/- E-y) to the bond-path. The +/- E-x-fields and +/- E-y-fields are separately applied to the Li-2 molecular graph until the bond ruptures. The next generation quantum theory of atoms in molecules (NG-QTAIM) interpretation of bonding was constructed with the stress tensor sigma(r) eigenvectors on the Hessian of rho(r) molecular graph. The asymmetry induced by both the +/- E-y-field and +/- E-x-field was detected in terms of the rotation of the orthogonal triad of stress tensor sigma(r) eigenvectors {(e) under bar (1 sigma), (e) under bar (2 sigma), (e) under bar (3 sigma)} relative to the Cartesian coordinate frame. The orthogonal triad of Hessian of rho(r) eigenvectors {(e) under bar (1), (e) under bar (2), (e) under bar (3)} however, were only able to detect rotation induced by the high degree of asymmetry present for bent bond-paths induced by the +/- E-y-fields. Larger movement of the NNAs along the bond-path correlated with greater bond critical point (BCP) bond metallicity xi(r(b)). The effect of applying the +/- E-x-field was compared with unpublished results on neutral Li-2 subject to a stretching distortion. The lack of NNA motion along the bond-path for the stretching distortion correlated with a lower degree of bond metallicity xi(r(b)). The stress tensor sigma(r) eigenvectors have a unique ability to detect rotation relative to the Cartesian coordinate frame for high bond-path symmetry occurring for the bond-stretching distortion and application of the +/- E-x-field. Suggestions for future work are provided.

A nonionizing ultrafast laser pulse of 20-fs duration with a peak amplitude electric-field ±E = 200 × 10-4 a.u. was simulated. It was applied to the ethene molecule to consider its effect on the electron dynamics, both during the application of the laser pulse and for up to 100 fs after the pulse was switched off. Four laser pulse frequencies ω = 0.2692, 0.2808, 0.2830, and 0.2900 a.u. were chosen to correspond to excitation energies mid-way between the (S1 ,S2 ), (S2 ,S3 ), (S3 ,S4 ) and (S4 ,S5 ) electronic states, respectively. Scalar quantum theory of atoms in molecules (QTAIM) was used to quantify the shifts of the C1C2 bond critical points (BCPs). Depending on the frequencies ω selected, the C1C2 BCP shifts were up to 5.8 times higher after the pulse was switched off compared with a static E-field with the same magnitude. Next generation QTAIM (NG-QTAIM) was used to visualize and quantify the directional chemical character. In particular, polarization effects and bond strengths, in the form of bond-rigidity vs. bond-flexibility, were found, for some laser pulse frequencies, to increase after the laser pulse was switched off. Our analysis demonstrates that NG-QTAIM, in partnership with ultrafast laser irradiation, is useful as a tool in the emerging field of ultrafast electron dynamics, which will be essential for the design, and control of molecular electronic devices.

We used next-generation QTAIM (NG-QTAIM) to explain the cis-effect for two families of molecules: C2X2 (X = H, F, Cl) and N2X2 (X = H, F, Cl). We explained why the cis-effect is the exception rather than the rule. This was undertaken by tracking the motion of the bond critical point (BCP) of the stress tensor trajectories Tσ(s) used to sample the Uσ-space cis- and trans-characteristics. The Tσ(s) were constructed by subjecting the C1-C2 BCP and N1-N2 BCP to torsions ± θ and summing all possible Tσ(s) from the bonding environment. During this process, care was taken to fully account for multi-reference effects. We associated bond-bending and bond-twisting components of the Tσ(s) with cis- and trans-characteristics, respectively, based on the relative ease of motion of the electronic charge density ρ(rb). Qualitative agreement is found with existing experimental data and predictions are made where experimental data is not available.

We used the recently introduced stress tensor trajectory Uσ space construction within the framework of next-generation quantum theory of atoms in molecules (NG-QTAIM) for a chirality investigation of alanine when subjected to a non-structurally distorting electric field. The resultant sliding of the axial-bond critical point (BCP) responded significantly, up to twice as much, in the presence of the applied electric field in comparison to its absence. The bond flexing, a measure of bond strain, was always lower by up to a factor of four in the presence of the electric field, depending on its direction and magnitude. An achiral character of up to 7% was found for alanine in the presence of the applied electric field. The achiral character was entirely absent in the presence of the lowest value of the applied electric field. Future applications, including molecular devices using left and right circularly polarized laser pulses, are briefly discussed.