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Abstract In this work, the Coulson‐Longuet‐Higgins response function (atom‐atomic polarizabilities [AAPs]) is used to describe the transfer of an electron perturbation in π‐conjugated systems in the presence of a static electric field. Computations are performed using different many‐electron approaches to study the effect. An accurate account of the electron correlation is shown to play a key role in the description of the interaction of a π‐shell with the external electrostatic field. Studies in this work reveal that the Hückel theory widely used in calculations of electron‐perturbation transfer is not reliable even at the qualitative level to describe the effects studies in this work. However, the π‐electron coupled cluster theory has been proven capable of providing a reliable electronic structure (among them, AAPs and excitation energies) that agree with the results obtained with the π‐electron full configuration‐interaction approach. The calculations also show that these properties have an essentially nonlinear character in terms of the strength of the applied electric field. The results obtained in the present work can provide useful information relevant to the application of π‐conjugated systems in molecular electronics. 

Laser-induced molecular alignment is well understood within the framework of the Born–Oppenheimer (BO) approximation. Without the BO approximation, however, the concept of molecular structure is lost, making it hard to precisely define alignment. In this work, we demonstrate the emergence of alignment from the first-ever non-BO quantum dynamics simulations, using the HD molecule exposed to ultrashort laser pulses as a few-body test case. We extract the degree of alignment from the non-BO wave function by means of an operator expressed in terms of pseudo-proton coordinates that mimics the BO-based definition of alignment. The only essential approximation, in addition to the semiclassical electric-dipole approximation for the matter–field interaction, is the choice of time-independent explicitly correlated Gaussian basis functions. We use a variational, electric-field-dependent basis-set construction procedure, which allows us to keep the basis-set dimension low while capturing the main effects of electric polarization on the nuclear and electronic degrees of freedom. The basis-set construction procedure is validated by comparing with virtually exact grid-based simulations for two one-dimensional model systems: laser-driven electron dynamics in a soft attractive Coulomb potential and nuclear rovibrational dynamics in a Morse potential.