C _n ( n =2−4): current status

Abstract

The major aspects of the C, C and C elemental carbon clusters are surveyed. For C, a brief analysis of its current status is presented. Regarding C, the most recent results obtained in our group are reviewed with emphasis on modelling its potential energy surface which is particularly complicated due to the presence of multiple conical intersections. As for C, the most stable isomeric forms of both triplet and singlet spin states and their possible interconversion pathways are examined afresh by means of accurate calculations. The main strategies for modelling the ground triplet C potential are also discussed. Starting from a truncated cluster expansion and a previously reported DMBE form for C, an approximate four-body term is calibrated from the energies. The final six-dimensional global DMBE form so obtained reproduces all known topographical aspects while providing an accurate description of the C linear-rhombic isomerization pathway. It is therefore commended for both spectroscopic and reaction dynamics studies.This article is part of the theme issue 'Modern theoretical chemistry'.

Reference Energies for Double Excitations

“…Here, we consider the linear geometry which has been found to be the most stable isomer, although the potential energy surface around this minimum is known to be particularly at. 181 Similarly to C 2 , we have studied two transitions -1 1 Σ + g → 1 1 ∆ g and 1 1 Σ + g → 2 1 Σ + g -which also both involve excitations from the occupied π CC orbitals to the vacant σ CC orbitals. ese lie higher in energy than in the dimer but remain energetically close to each other.…”

Publisher Correction to: Even numbered carbon clusters: cost-effective wavefunction-based method for calculation and automated location of most structural isomers

“…No comparison is possible with a VT Z basis, since M06-2X does not predict such a saddle point; a similar finding is reported by Ngandjong et al [19] with M06-2X/AVDZ. Of course, the above remarkable agreement may have been somewhat accidental as the CASDC/CBS(T, Q) estimate [9] for the relative stability of the cyclic vs linear forms places the latter only 6.14 kcal mol −1 above the former, a value smaller by ∼50 % than VOS-MP2/CBS(d, t) and nearly four times smaller than M06-2X [19].…”

“…The calculations here reported entail two parts. The first aims at validation of the method by testing its reliability on singlet C 4 which we have studied elsewhere at high levels of ab initio theory [9]. For this, we consider the conversion of rhombic (r − C 4 ) into linear ( − C 4 ) isomeric Fig.…”

“…The smaller play a key role in the chemistry of carbon rich stars, comets, and interstellar molecular clouds, while acting as building blocks in forming complex carbon-containing compounds. Added to this panoplia of astrophysical significance, they are of interest in connection with the formation of fullerenes, nanotubes, carbon-rich thin films, and the predominant species in terrestrial sooting flames; the bibliography is vast, with the reader addressed to a few papers [1][2][3][4][5][6][7][8][9] from which others may be obtained by cross-referencing. All the above finds justification on the exceptional bonding properties of carbon and its unique ability to form single, double, and triple (eventually quadruple in the dimer [10]) bonds.…”

“…Naturally, elucidation of the possible mechanisms leading to formation and growth of C n aggregates can only be done once the properties of the smaller ones have been clarified [6]. However, the existence of nearly isoenergetic isomers, a high-density of low-lying singlet and triplet electronic states, and a significant multi-reference character, makes their study theoretically most challenging [8,9].…”