The structures and properties of linear carbon clusters and molecules formed by chemisorption of hydrogen and lithium on carbon aggregates

Three groups of molecules, (1) linear carbon clusters C{dollar}sb{lcub}rm n{rcub}{dollar} (n = 2-10), (2) linear HC{dollar}sb{lcub}rm n{rcub}{dollar}H molecules (n = 2-10), and (3) linear LiC{dollar}sb{lcub}rm n{rcub}{dollar}Li molecules (n = 2-8), have been studied using ab initio RHF SCF methods. Total energies, cohesive and chemisorption energies, the geometric and electronic structures, and gross charge distributions have been predicted.; For the first group of molecules, we confirm that: (1) they have cumulene-type bonding; (2) all odd-number clusters have a {dollar}rm sp{lcub}1{rcub}Sigmasbsp {lcub}g{rcub}{lcub}+{rcub}{dollar} ground state, all even-number clusters have a {dollar}rm sp{lcub}3{rcub}Sigmasbsp {lcub}g{rcub}{lcub}-{rcub}{dollar} ground state; (3) odd-number clusters are more stable than their neighboring even-number clusters; (4) the individual bond energies of each cluster indicate that C{dollar}sb3{dollar}, C{dollar}sb5{dollar}, and C{dollar}sb7{dollar} would be the most abundant species upon dissociation; (5) charge alternation is more pronounced for the odd-number clusters.; For the latter two groups of molecules the chemisorption of hydrogen and lithium on each end of a cluster causes considerable change both energetically and structurally. It is shown that: (1) the added H and Li atoms stabilize carbon clusters, especially the even-number species; (2) the bonding structures for the even-number molecules are polyyne-type; (3) the binding energies have an alternating pattern with the even-number molecules having stronger bonds than their neighboring odd-number species; (4) the charge distributions are very pronounced toward the H-C or Li-C bonds and become "smoother" in the central bonding regions; (5) the inclusion of polarized orbitals in the basis set significantly lowered the energies, especially for HC{dollar}sb{lcub}rm n{rcub}{dollar}H molecules, suggesting the importance of d orbitals on carbon and p orbitals on hydrogen and lithium in accounting for bonding; (6) all even-number molecules have a {dollar}rm sp{lcub}1{rcub}Sigmasbsp {lcub}g{rcub}{lcub}+{rcub}{dollar} ground state, all odd-number molecules have a {dollar}rm sp{lcub}3{rcub}Sigmasbsp {lcub}g{rcub}{lcub}-{rcub}{dollar} ground state.; Also investigated in this work are several non-linear LiC{dollar}sb2{dollar}Li and LiC{dollar}sb3{dollar}Li isomers.