Binding energies of small lithium clusters: A comparison of different theoretical calculations

In order to compare different calculations used in theoretical studies on lithium clusters, we have calculated the binding energies of small lithium clusters using all electron diffusion quantum Monte Carlo (DMC) simulation, coupled-cluster (CCSD(T)) approach, as well as density functional theory (DFT) with different exchange-correlation (xc) functionals. The obtained DMC results are in very good agreement with available experimental data and with CCSD(T) calculations. However, the DFT results depend strongly on the approximations for the xc functional. Furthermore, considering the DMC result as a benchmark, we obtain the electron correlation energy of the clusters and quantify its contribution to the binding energies.