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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. 

We report high-accuracy calculations of the ground and the lowest eight excited ${}^{2}P^o$states of the two stable isotopes of the boron atom, ${}^{10}\mathrm{B}$and ${}^{11}\mathrm{B}$, as well as of the boron atom with an infinite nuclear mass ${}^{\infty }\mathrm{B}$. The nonrelativistic wave function of each of the states is generated in an independent variational calculation by expanding it in terms of a large number, $12000–17000$, of all-electron explicitly correlated Gaussian (ECG) functions whose nonlinear parameters are extensively optimized with a procedure that employs analytic energy gradient determined with respect to these parameters. These highly accurate wave functions are used to compute the fine-structure splittings using the first order of the perturbation theory $(\sim {\alpha }^2)$, where $\alpha$is the fine-structure constant, which are then corrected for the electron magnetic moment anomaly $(\sim {\alpha }^3)$. As the nonrelativistic Hamiltonian explicitly depends on the mass of the nucleus, the recoil corrections up to the order of ${\alpha }^2$are automatically accounted for in the fine-structure calculations. Furthermore, the off-diagonal corrections to the fine structure $(\sim {\alpha }^4)$are estimated using the multireference methods based on one-electron Gaussian orbitals. The results obtained in this paper are considerably more accurate than those available in the literature. Moreover, we report accurate splittings for a number of excited ${}^{2}P^o$states, for which there have been no reliable experimental or theoretical data at all. The calculated values presented in this paper may serve as a valuable guide for future experimental measurements of the fine structure of the boron atom. As the fine structure of an atom provides a spectral signature that can facilitate atom's detection, our data can also aid the search for trace amounts of boron in the interstellar medium. Published by the American Physical Society2024