Electronic excitations of stable fullerene-like GaP clusters
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U3.4.1
Electronic excitations of stable fullerene-like GaP clusters Giuliano Malloci 1,2, Giancarlo Cappellini 2,3, Giacomo Mulas1 and Guido Satta 2,3 1 INAF-Osservatorio Astronomico di Cagliari, Strada n. 54, Località Poggio dei Pini, I-09012 Capoterra (CA), Italy 2 Dipartimento di Fisica, Università degli Studi di Cagliari, Strada Provinciale Monserrato-Sestu Km 0.700, I-09042 Monserrato (Ca), Italy 3 INFM-Sardinian Laboratory for Computational Materials Science (SLACS), Strada Provinciale Monserrato-Sestu Km 0.700, I-09042 Monserrato (Ca), Italy
ABSTRACT We present quasi-particle (QP) corrections to the electronic energies for small GaP fullerenes, a new class of nanoscaled materials predicted to be stable and to show spontaneous formation. Using Time-Dependent Density Functional Theory we also computed the optical absorption spectra. The comparison between single-particle and optical absorption spectra yields strong excitonic effects with bonding energy up to 3.5 eV. The QP corrected HOMO-LUMO energy gaps confirm the high stability predicted for such molecules using ground-state computational schemes. The present results can be useful to identify the successful synthesis of these systems via optical absorption and QP spectra. INTRODUCTION Since the discovery of fullerenes [1] and nanotubes [2], the search for new nanoscaled materials based on elements other than carbon has received much attention. One interesting question, related to future developments of nanoscience and nanotechnology, is whether typical semiconductors of the III-V family such as GaP or GaAs, which do not possess a graphitic bulk phase, are able to form hollow fullerene-like structures. Along these lines, recent Density Functional Theory (DFT) and Car-Parrinello molecular dynamics simulations [3] suggested the possible existence of III-V fullerene clusters with 20 and 28 atoms, with the same topology as C20 and C28 fullerenes. These molecules are predicted to be characterised by stable structures with very symmetric equilibrium geometries (Th and Td symmetry point group), high thermal stability up to a temperature of 1500-2000 K, high chemical stability (large HOMO-LUMO energy gaps and closed-shell electronic structures) and stability against positive and negative ionizations. The above properties were shown to be common to all the III-V compounds, namely GaAs, AlAs and AlP [4]. These studies therefore opened the real possibility to find an experimental procedure apt to prepare these new nanoscaled materials in macroscopic amounts. AIM AND THEORETICAL METHODS Optical spectroscopy has been recently proposed to unambiguously elucidate the ground state of the different isomers of C20, the smallest fullerene [5]. Should an experimental procedure be found which may synthesise small fullerene-like GaP clusters, optical absorption spectra could be likewise used to distinguish between different newly formed isomers. The use of Kohn-
U3.4.2
Sham eigenvalues within DFT to determine the quasi-particle (QP) properties of many-electrons systems yields
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