been assumed that both the tubular systems and molecules placed
inside them were oriented along the z-axis.
It is well established that in order to obtain reliable values of
molecular (hyper)polarizabilities a proper method including electron correlation and extended basis set should be used (see Refs.
[78–81] and the references cited therein). In this study, all
calculations of the electric-dipole properties have been carried
out using the MP2 method combined with the medium-sized
6-31++G (d,p) basis set. This choice is determined by the size of the
largest molecular complexes included in this comparative study.
Due to the lack of theoretical as well as experimental data regarding (hyper)polarizabilities of studied complexes, the results of our
recent state-of-the-art calculations for the LiH molecule in the confined environments are taken as a reference[22,54,55]. Moreover,
in order to confirm that the selected computational methodology
provides reliable estimates of investigated electric properties we
have also carried out the test calculations for the LiH molecule confined by the harmonic oscillator potential as well as helium nanotubes. The obtained results are collected in Tables 1 and 2. The
analysis of the MP2/6-31++G (d,p) results leads to the conclusion
that this level of theory is sufficient for semiquantitative analysis.