On the nonlinear electrical properties of molecules in confined spaces – From cylindrical harmonic potential to carbon nanotube cages

On the directional character of orbital compression: A model study of the electric properties of LiH–(He) complexes

“…In fact, helium is the least polarizable as well as the smallest (considering its atomic radius), the most difficult to ionize, the hardest (in Pearson's scale) and the most electronegative atom known [38]. This makes He atoms particularly suitable for model studies concerning the pure spatial confinement effect, what has been shown in several theoretical studies in the past [14,19,22,[39][40][41][42][43][44]. Additionally, due to the unique properties of helium atom it was also used for defining hardness of molecular surface and its descriptor [45][46][47][48].…”

“…Such an idea has a long history and allowed to obtain a lot of valuable information about the electronic structure and one-electron properties of various atomic and molecular systems as well as nanoscale objects [1,2,5,9,10]. Alternatively, the supermolecular (SM) approximation together with the concept of interaction-induced properties constitute an important formalism in the analysis of properties of the spatially confined molecular systems (see [8,[19][20][21][22] and references therein). Furthermore, quite recently, Cammi et al developed an original quantum chemical technique for the calculations of equilibrium geometry and vibrational frequencies of molecular systems in condensed phases at high pressures [23][24][25].…”

“…Due to the fact that LiH is a small molecule containing only four electrons, it constitutes an ideal system for the highly accurate calculations at different levels of theoretical approximations, including the explicitly correlated wave functions, configuration interaction (CI) as well as coupled cluster (CC) methods. The set of reference data available for this particular molecule contains, among others, the electronic and vibrational contributions to dipole moment and (hyper)polarizabilities, determined within both nonadiabatic and Born-Oppenheimer approximations [18,19,22,[73][74][75][76][77][78][79][80][81][82][83][84][85][86][87][88][89][90]. Moreover, the dipole moment of LiH in the first bonded excited state (A 1 Σ + ) is much smaller (and of the opposite sign) than that in the ground state, what indicates the presence of charge-transfer state.…”

“…It is well established that the occurrence of the CT state is a crucial factor increasing the nonlinear optical response of molecular systems to external electric field. According to the above, the LiH molecule seems to be an excellent system for model theoretical analysis in the field of molecular nonlinear optics, including studies concerning the effect of spatial restriction on its linear and nonlinear electric properties [18,19,22,73,74]. In contrast to the above cited papers, the present study has been designed in such a manner to elucidate the directional character of orbital compression on the magnitude of exchange-repulsion energy as well as electric response of the LiH molecule spatially confined by helium atoms.…”

“…The main objective of the present work, being addendum and extension of our earlier studies [18,19,22,32,33,39], is to explore the static electric properties of spatially confined LiH molecule in its ground singlet electronic state (X 1 Σ + ). Due to the fact that LiH is a small molecule containing only four electrons, it constitutes an ideal system for the highly accurate calculations at different levels of theoretical approximations, including the explicitly correlated wave functions, configuration interaction (CI) as well as coupled cluster (CC) methods.…”