In the above equationsEðFiÞstands for the energy of a system in the
presence of an electric field in the directioni (i¼x;y;z). The electric-field amplitude equal to 0.001 au was set during the calculations. This value was chosen based on stability checks of the
numerical differentiation, performed with the aid of the Romberg–Rutishauser (RR) scheme[75,76]. Considering that (i) longitudinal components usually determine the orientationally averaged
electric properties of molecules of axial symmetry, (ii) off-diagonal
components are expected to diminish rapidly upon confinement,
we focus solely in this study onazz andbzzz
.
In order to describe the effect of confinement on the electric-dipole properties of investigated molecules, two models were employed – both corresponding to cylindrical topology of confining
environment. The first one employs a harmonic oscillator potential