The Evolution of Bonding and Thermodynamic Properties of Boron‐Doped Small Carbon Clusters: An Ab Initio Study

Abstract

Theoretical studies on BC(n) (n=1-6) clusters are carried out using density functional theory, Møller-Plesset second-order perturbation theory (MP2), coupled-cluster calculations including up to triple excitations (CCSD(T)), and higher-level approaches. All possible isomers depending on the positions of the boron atom are generated and the lowest-energy isomers are determined for doublet and quartet electronic states. The three potential evolution paths of the clusters are determined as a function of their size. The energetic and electronic consequences for the increased size of structures differ significantly, which leads to representatives of the ground electronic state from different structural groups. The ab initio calculated thermal functions allow enhancements to the available atomization energies and improve the agreement between the calculated and experimental heat content.

Electronic Structures and Thermochemical Properties of the Small Silicon‐Doped Boron Clusters BnSi (n=1–7) and Their Anions

“…The Si atom prefers the external position of the skeleton and tends to form bonds with its two neighboring B atoms. The larger B 7 Si cluster is constructed by doping Si-atoms on the symmetry axis of the B n host, which leads to the bonding of the silicon to the ring boron atoms through a number of hyper-coordination. Calculations of the thermochemical properties of B n Si 0/À clusters, such as binding energies (BE), heats of formation at 0 K (DH f 0 ) and 298 K (DH f [298] ), adiabatic (ADE) and vertical (VDE) detachment energies, and dissociation energies (D e ), are performed using the high accuracy G4 and complete basis-set extrapolation (CCSD(T)/CBS) approaches.…”

“…The planar structures are dominant for small B n Si clusters with n 5. The B 6 Si molecule represents a geometrical transition with a quasiplanar geometry, and the first 3D global minimum is found for the B 7 Si cluster. The small neutral B n Si clusters can be formed by substituting the single boron atom of B n + 1 by silicon.…”

“…Unlike the B n C clusters where the B 7 C was reported to be a planar structure (C s ), [54] the global minimum of B 7 Si is a 3D structure 7 n.1 (C 2v , 2 B 1 ) that is distorted from a high symmetry form (C 6v ), with Si located on the C 6 axis of a bi-capped hexagonal ring. The planar "ribbon" structure 7 n.2, having a similar shape to the global minimum B 7 C, is the second isomer with a relative energy of 7.4 kcal mol À1 .…”

“…Other planar forms 7 n.3 and 7 n.4 rather represent transition states. Following attachment of one excess electron, the high symmetry 7 a.1 (C 6v ) becomes the global minimum of B 7 Si À . 7 a.2 (C s ) turns out to be the second isomer with relative energy of 7.4 kcal mol…”

“…The first 3D global minimum in the series of B n Si is found for B 7 Si. Unlike the B n C clusters where the B 7 C was reported to be a planar structure (C s ), [54] the global minimum of B 7 Si is a 3D structure 7 n.1 (C 2v , 2 B 1 ) that is distorted from a high symmetry form (C 6v ), with Si located on the C 6 axis of a bi-capped hexagonal ring.…”