Collective resonances of the molecule: effects of electron-density profile

Abstract

Previously, we discussed a purely classical model for analysing surface plasmons of the C 60 molecule. The molecule was described as an abrupt spherical shell containing an effective number of π or π + σ electrons. This simple model was found to be quite applicable for analysis of electron energy loss spectra (EELS), describing the main features of the experimentally observed collective resonances of electrons. In this study we have extended our earlier classical model using spherically averaged radial charge distributions of C 60 constructed using different numbers of valence electrons. These charge distributions have been obtained from a self-consistent local density calculation, based on a molecular-orbital linear combination of atomic orbitals (MO-LCAO) approach. Use of this type of smooth charge distribution introduces, together with causality, a natural broadening of the collective resonances.

Hydrodynamic model of the collective electron resonances in C60 fullerene

“…The found solution generalizes the one obtained for the plasma shell without allowance for the spatial dispersion [12,13] and passes to it in the formal limit 0 →…”

“…However, under parameters values corresponding to the C 60 molecule, when these lengths are of the same order, both these plasmons (providing the main contribution to the fullerene absorption spectrum) are found to be actually volume ones in their spatial structure, and the frequency of the higher of them becomes larger than the plasma frequency (as with all the higher volume plasmons). The resonance curve of the fullerene absorption cross-section calculated on the basis of the developed model with allowance for the surface losses caused by the reflection of electrons at the shell boundaries agrees satisfactorily with the experimental data.Studies on the dynamical polarizability of the spherical plasma shells interacting with the fields of different external sources are of interest in connection with the problems of the observed scattering and absorption spectra identification of the fullerenes (and, in particular, C 60 molecule), displaying oscillatory features of plasma-like systems due to a great number of the valence (delocalized) electrons [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. Related circle of problems arises also when studying metamaterials made on the basis of shell-like structures (for example, semiconductor quantum dots or metal-dielectric nanoparticles) [19][20][21][22][23][24][25][26][27].…”

Dynamical Screening of an Endohedral Atom

“…As observed in [31,32] and seen in other theoretical works on these plasmon modes of the fullerene (e.g. [22,33]), the antisymmetric mode does not generally manifest itself as strongly as the other mode.…”

Disentangling multipole contributions to collective excitations in fullerenes

“…Particle-hole (p-h) excitations and collective modes may "live" in overlapping momentum-energy domains and couple in a size-dependent way that cannot be understood classically [9][10][11]. Giant plasmon resonances were measured in buckminster fullerene C 60 [12][13][14][15][16][17] and explained, e.g., by assuming C 60 to have a constant density of electrons confined to a shell with inner (R 1 ) and outer (R 2 ) radii (the spherical shell model) [18][19][20]. Refinements in terms of a semi-classical approximation (SCA) incorporate the quantum-mechanical density extending out of the shell R 1 < r < R 2 (so-called spill-out density [21]).…”