A Density Functional Study on Beryllium-Doped Carbon Dianion Clusters C_nBe^2- (n = 4−14)

Abstract

Making use of the software of molecular graphics, we designed numerous models of C(n)()Be(2-) (n = 4-14). We carried out geometry optimization and calculation on vibration frequency by means of the B3LYP density functional method. After comparison of structure stability, we found that the ground-state isomers of C(n)()Be(2-) (n = 4-14) are linear with the beryllium atom located inside the C(n)() chain. When a side carbon chain is with an even number of carbon atoms, it is polyacetylene-like, whereas when a side chain is with an odd number of carbon atoms, it is cumulene-like. The C(n)Be(2-) (n = 4-14) clusters with an even number of carbon atoms are more stable than that with an odd number of carbon atoms, matching the peak pattern observed in accelerator mass spectrometry (AMS) and Coulomb Explosion Imaging (CEI) investigations of C(n)()Be(2-) (n = 4-14). The trend of such odd/even alternation is explained based on concepts of bonding characteristics, electronic configuration, electron detachment, and incremental binding energy.

Parity alternation of linear ground-state CnS2− (n=6–18) clusters

“…Trindle and Yumak developed a set of small open shell dianions stable, their results of B3LYP/6-31+G(d) description of the carbene-based systems are in impressive agreement with ROMP and CCSD calculations on the same basis, and they considered that the calculations in a modest basis and in the B3LYP variant of DFT are trustworthy [31]. In the study on C n Be 2− (n = 4-14), we also performed B3LYP/6-311+G * calculations on the structures and energies of the clusters [32]. In the present studies, we examined many isomers and made comparison for the identification of the "ground-state" isomers, and focused on the common trends of odd/even parity alternation.…”

“…After comparing a great number of models, we find that the "ground-state" isomers of C n S 2− (n = 6-18) clusters are linear in configuration having a sulfur atom at a terminal position. For the beryllium-doped carbon dianion clusters C n Be 2− (n = 4-14), the linear configuration with the beryllium atom located at the end of a carbon chain is not the most stable isomers; those found with the lowest energy are having the beryllium atom located inside the carbon chain [32].…”

“…The strong force of Coulomb repulsion of a doubly charged anion would either enhance the emission of an electron or promote the decomposition of the molecular framework into two monoanionic fragments [21]. For the C n Be 2− (n = 4-14) clusters, the dianionic structures with the beryllium atom located inside the carbon chain are more stable than those with the beryllium atom located at the end of the carbon chain, because the interior beryllium atom plays an important role of reducing Coulomb repulsion by separating the two negative charges [32]. According to the NBO atomic charges shown in Table 2, the majority of negative charge is located on the sulfur atom and the two carbon atoms at the other end of the carbon chain.…”

“…The two negative charges located at the two terminuses of the chain could obviously reduce the Coulomb repulsion force and stabilize the linear structure. The sulfur is more electron-rich than the carbon atom, it helps to seal the terminal of the carbon chain, while beryllium is an electron-deficient element and is unlikely to be a terminal atom in the C n Be 2− (n = 4-14) clusters [32]. When n is odd, the carbon atom at the end has two unpaired electrons and triplet structures are favorable.…”

“…Klein [31]. Earlier, we carried out a B3LYP density functional study on beryllium-doped carbon dianion C n Be 2− (n = 4-14) clusters [32].…”