The electronic structure of small sodium clusters

Ab initio molecular orbital calculations using the STO3-21G basis set has been carried out for the cluster series Na n + , Na n , and Na n - (wheren=2-7). The basis set is shown to be reliable compared with more extensive basis sets at the Hartree-Fock level. Thirty-one optimized structures are reported and discussed, many of which (especially for the anions) have not been considered. The STO3-21G//STO3-21G calculations suggest that for most of the species the optimum geometries are planar. In particular, the optimized structures for the anionic species should provide a starting point for more sophisticated configuration interaction calculations

Structural and energetic trends in Group-I and II hydrohelide cations

The ground states of HMHe⁺ (M = Li, Na, K) and HMHe²⁺ (M = Be, Mg, Ca) have been investigated using relativistically-corrected CCSD(T) and IC-MRCI. The HLiHe⁺, HBeHe²⁺, HNaHe⁺ and HMgHe²⁺ ions were found to be linear in the ground state. Conversely, HKHe⁺ and HCaHe²⁺ were quasi-linear, with ²A'²Σ⁺ barrier heights of ca. 2 and 5 cm⁻¹, respectively. Structural and energetic trends are consistent with H and He sharing covalent and electrostatic bonds with the metal ion, respectively. These trends are also seen to be strictly dependent on the polarisability of the central metal ion

Trends in low-lying electronic states of XH₂ (X = Li, Na, K)

Relativistically-corrected CCSD(T), IC-MRCI and IC-MRCI+ Q have been employed in an investigation of low-lying states of LiH₂, NaH₂ and KH₂. The lowest ²A₁ and ²∑⁻ states were found to be purely repulsive, in agreement with previous predictions. Equilibrium structures of the ²B₂, ²B₁ and ²∑g⁺ states have been calculated and are in good agreement with available theoretical data. For the C₂v species the main factor determining the structure and stability was the relative orientations and occupations of the valence p atomic orbital of the metal and the H₂ 1σg orbital. The presence of occupied p orbitals in the metal ligand increased the stability of the D∞h species. Spectroscopic parameters of the ²B₂, ²B₁ and ²∑g⁺ states of KH₂ are reported here for the first time