Quantum chemical study of lithium–C60 clusters

Zimmermann, Uwe; Burkhardt, A.; Malinowski, N.; Näher, U.; Martin, T. P.

doi:10.1063/1.467664

Cited by 41 publications

(21 citation statements)

References 23 publications

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“…30,31 For alkaline earth materials it is now commonly accepted that many atoms homogeneously surround the C 60 molecule in spherically centred shells. For other metals, such as lithium 5,11,12,21 a strong charge transfer takes place with carbon and the resulting ionic interaction may be stronger than the metallic bonding. As a consequence, homogeneous coating of C 60 is also observed at low coverage.…”

Section: Introductionmentioning

confidence: 99%

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Nucleation of a sodium droplet onC60

et al. 2003

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We investigate theoretically the progressive coating of C60 by several sodium atoms. Density functional calculations using a nonlocal functional are performed for NaC60 and Na2C60 in various configurations. These data are used to construct an empirical atomistic model in order to treat larger sizes in a statistical and dynamical context. Fluctuating charges are incorporated to account for charge transfer between sodium and carbon atoms. By performing systematic global optimization in the size range 1 ≤ n ≤ 30, we find that NanC60 is homogeneously coated at small sizes, and that a growing droplet is formed above n ≥ 8. The separate effects of single ionization and thermalization are also considered, as well as the changes due to a strong external electric field. The present results are discussed in the light of various experimental data.

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Section: Introductionmentioning

confidence: 99%

“…[17][18][19][20][21][22][23][24][25][26][27][28][29] Coverage of fullerenes with semiconductor atoms or clusters has also been investigated. 30,31 For alkaline earth materials it is now commonly accepted that many atoms homogeneously surround the C 60 molecule in spherically centred shells.…”

Section: Introductionmentioning

confidence: 99%

Nucleation of a sodium droplet onC60

et al. 2003

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“…The deviations from the icosahedral shape correspond to symmetry breakings which may induce important modifications in the energy sequence and degeneracies of the one-electron levels, thereby affecting the optical properties. On the other hand, metallic screening is also expected to become increasingly important, due to the mobile valence electrons of the metal coating atoms, which will fill the weakly bound states of the cluster.The symmetry breaking effect has been conjectured [3] in order to interpret the abundance spectra of alkalicoated fullerenes, and corroborated by the results of the simulations carried out by Martin's group [4]. In this context, Li C is a very special cluster, since it is the only cluster predicted so far to maintain the symmetry of the fullerene seed.…”

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confidence: 76%

“…The lithium coating experiments confirmed the special stability of the Li C cluster, which develops also a well defined peak in the mass spectra of singly and doubly ionized lithium-coated C clusters. Theoretically, a good deal is known about the structural properties of Li C [2], as well as other lithiumcoated fullerenes [4]. This is not the case concerning their optical properties, which are expected to display a sizedependent behaviour.…”

Section: Introductionmentioning

confidence: 97%

Monolayer metal coverage of fullerenes: the optical response

Pacheco

Alasia

Roman

et al. 1996

Z Phys D - Atoms, Molecules and Clusters

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A first-principles investigation of the photoabsorption cross section of the specially stable cluster Li C is carried out, including the icosahedral symmetry of the cluster and treating the ions via ab initio pseudopotentials. The role of the coating metal is assessed by computing the same quantity for the fullerene ''seed''. It is found that the main absorption features are determined by the carbon molecule, both at low and high excitation energies, in spite of a reduction of 60% for the ionization threshold of Li C as compared to C . Nonetheless the lithium coating is responsible for small yet clearly observable effects throughout the spectrum, in particular for a more structured and broad strength distribution at excitation energies below the ionization threshold of C , and a double peak structure in the Mie resonance at 20 eV.PACS: 36.40. #d; 31.50. #w; 33.20.Kf Inspired by electrochemical evidence of a stable Li C phase [1], the cluster Li C has been predicted to be particularly stable, due to the favourable combination of a closed-shell electronic structure, realized in a highlysymmetric icosahedral geometry [2]. This structural property is a somewhat surprising result, because with other alkali elements saturation occurs at x"6 for the intercalated compounds M V C . Prompted by these results, T. P. Martin and his group co-evaporated C and different alkali metals in a gas aggregation cell, registering the mass spectrum for several types of C clusters coated with metal atoms [3]. The lithium coating experiments confirmed the special stability of the Li C cluster, which develops also a well defined peak in the mass spectra of singly and doubly ionized lithium-coated C clusters. Theoretically, a good deal is known about the structural properties of Li C [2], as well as other lithiumcoated fullerenes [4]. This is not the case concerning their optical properties, which are expected to display a sizedependent behaviour. In fact, by increasing the number of alkali coating atoms, it is likely that the cluster undergoes a non-metal to metal transition, in which the C cage becomes the seed for a metallic nanostructure. Qualitatively, and taking as a reference the optical spectrum of the isolated C cage, one may expect that alkali coverage will induce important effects in the low-energy region (0(E(6 eV) of the absorption spectrum, where the collective charge density oscillations of alkali clusters take place, whereas at higher excitation energies (E 20 eV) the spectrum will be characterized by a (strongly screened) bump which originates in the so-called Mie plasmon [5] of C . Several physical phenomena may lead to such effects. On one hand, the layers of alkali-coating atoms will induce, in general, new geometrical equilibrium shapes for these clusters, as compared to the icosahedral shape of the C fullerene. The deviations from the icosahedral shape correspond to symmetry breakings which may induce important modifications in the energy sequence and degeneracies of the one-electron levels, thereby affecting the optic...

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“…The stability of this system was also confirmed by MNDO calculations. 17 In addition, the calculations of C60Li ~ complexes (for n varied from I to 14) 17 showed that at n < 9 the Li atoms are coordinated preferably to hexagonal faces, whereas at n > 9 coordination to pentagonal faces occurs.…”

Section: The Third Possible Procedures Of Stabilization Of C60mentioning

confidence: 98%

Simulation of molecular and electronic structure of η5-π-complexes of fullereneI h -C 60 with half-sandwich XCp species (X=Si, Ge, Sn)

Chistyakov

Станкевич

1998

Russ Chem Bull

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The molecular and electronic structure of hypothetical complexes of unsubstituted fullerene C6o with I h symmetry and its cyclopentadienyl type derivatives were simulated by the MNDO/PM3 method taking the C60(XCp) ~ molecules (n = 1, 2, 10, 12; X = Si, Ge, Sn) and qS-rc-C60HsXCp (X ---Ge, Sn), respectively, as example. The complexes 12qS-Tt-C60(XCP)12 and rls-n-Cts0HsXCp with lh and Csv symmetry, respectively, were found to be the most stable compounds. The energies of the X--C60 bonds in these complexes are close ~o those of X--Cp bonds in bis(cyclopentadienyl) complexes XCp2 and are substantially higher than the energies of similar bonds in complexes of unsubstituted fullerene q t-C60XC p" al~ rl5--x-C60XCp +. Geometric parameters and spin densities in radicals C60XC p" and biradicals C60(XCp) 2 and C60Hl0 were calculated.Key words: fullerenes, re-complexes, radicals; silicon, germanium, tin; quantum-chemical calculation, M N DO/PM3 method.The carbon framework of the polyhedral cluster C60 with I h symmetry (lh-C60) (as well as the polyhedra of many other fullerenes) consists of five-and sixmembered cycles, each of them containing 5 and 6 =-electrons, respectively. Because of this, there is a possibility for the cluster lh-C60 to form rlS-,'t -and rl6-Tc-complexes. However, no stable compounds of this type have been synthesized to date, though the fuUerene chemistry is progressing very intensively (see, e.g., Ref. 1).Theoretical estimates of the possibility for 35-and rl6-complexes of C60 to exist z-8 have been carried out first of all taking exohedral and endohedral C60 complexes with the Li + cation as examples (see Ref. 2). It has been shown by the MNDO method that the rl6-coordination of Li + to unsubstituted fullerene is more preferable than the rlS-coordination; however, the Li--C60 bond energy (taking into account the fact that this method overestimates the Li--C bond energy) 9 is low.The estimates of the stability of hypothetical complexes rl'l-C60MCp (M = Fe, Ru, Os) and rln-C60CrBz (n = 5, 6) obtained from EHT calculations with no geometry optimization show that the M--C60 bonds in such coml~lexes, if they exist, must be very weak as compared to the M--Cp bonds in the same complexes and in corresponding classical sandwich compounds MCp~ and MBz 2 with the same metals. 4`s Strong delocalization of ~-electrons in rl 5-and rl6-complexes of unsubstituted fullerenes C m (m > 60) is likely to be the main reason for the relatively low stability of these systems. 5 Previously, we have proposed three procedures for increasing the stability of rlS-complexes with polyhedral carbon framework. This procedure was first demonstrated taking bowl-shaped fullerene fragments as an example 6 and then applied to complexes C60R 5 (R = H, CI, Br) with SiCp" species (see Ref. 7) and Li atom (see Ref. 8). In this case the ~-el.ectron system of the radical C60R 5" (1) formed is divided into two parts consisting of 5 and 50 r~-electrons.The electron density on the atoms of the isolated pent* fragment increases and the net effe...

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Quantum chemical study of lithium–C60 clusters

Cited by 41 publications

References 23 publications

Nucleation of a sodium droplet onC60

Nucleation of a sodium droplet onC60

Monolayer metal coverage of fullerenes: the optical response

Simulation of molecular and electronic structure of η5-π-complexes of fullereneI h -C 60 with half-sandwich XCp species (X=Si, Ge, Sn)

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