Figure 1

The position of the pointlike atom, indicated by the filled circle, is confined at $\mathit{\rho }$ inside the fullerene. The angle between $\mathit{\rho }$ and the external field ${\mathbf{E}}_0$ is denoted $\theta$. The field at the position of the fullerene is given by ${\mathbf{E}}_{\text{tot}}\left(\mathit{\rho },\omega \right)$.Reuse & Permissions

Figure 2

(Color online) The dynamical screening factors for the centrally positioned endohedral atom: $\text{Ar}@{\text{C}}_{60}$ (top) and $\text{Mg}@{\text{C}}_{60}$ (bottom). The common legend is given in the top panel. The dynamical screening factors were calculated for two cases: from Eq. (20), which neglects the atomic feedback, labeled as “no $\alpha \left(\omega \right)$,” and from Eq. (19), with accounting for this feedback, labeled as “with $\alpha \left(\omega \right)$,” represented, respectively, by the solid and the dashed lines of medium thickness. These are compared with TDLDA calculations shown as thin blue (dark) solid lines from [18, 19]. The ionization potential of the endohedral atom is indicated by the dotted line. The thick solid and dashed lines represent the factors calculated within the modified model, which includes the contributions of the $\sigma$ and $\pi$ plasmons; see Eqs. (22, 21). The symmetric (s) and antisymmetric (a) modes of the $\pi$ and the $\sigma$ plasmons are indicated by arrows on the plot for $\text{Mg}@{\text{C}}_{60}$. Regions of particularly strong interference (“int.”), all negative, between the $\pi$ and the $\sigma$ plasmons are also indicated.Reuse & Permissions

Figure 3

(Color online) Left: the dynamic dipole polarizability of argon, calculated within the random-phase approximation with exchange (RPAE). The common legend is given in the right panel. Right: the dynamic dipole polarizability of magnesium, based on the scattering factors of [27]. The real part was calculated from the imaginary part of the polarizability via the dispersion relation. In both plots, the solid blue line is the real part and the dashed green line is the imaginary part. The first ionization threshold of the atom is indicated by the dotted line.Reuse & Permissions

Figure 4

(Color online) The dynamical screening factor for $\text{Ar}@{\text{C}}_{60}$ as a function of photon energy $\omega$ and the radial distance of the atom from the fullerene’s center, $\rho$, calculated for different values of the angle $\theta$ between $\mathit{\rho }$ and ${\mathbf{E}}_0$.Reuse & Permissions

Figure 5

(Color online) Same as Fig. 4 but for $\text{Ar}@{\text{C}}_{240}$.Reuse & Permissions

Figure 6

(Color online) The $U_{\text{vdW}}$ profiles for $\text{Ar}@{\text{C}}_{60}$ (left) and $\text{Ar}@{\text{C}}_{240}$ (right) are shown.Reuse & Permissions

Figure 7

(Color online) The spatially averaged dynamical screening factors for $\text{Ar}@{\text{C}}_{60}$ (left) and for $\text{Ar}@{\text{C}}_{240}$ (right) for $T=100\text{K}$ (thick solid line) and $T=1500\text{K}$ (thick dashed line). The common legend is shown in the left panel. The screening factor for the centrally positioned atom is shown for comparison (thin solid line). For $\text{Ar}@{\text{C}}_{60}$ this line coincides with the averaged screening factor at 100 K.Reuse & Permissions