Atomization Energy Calculations in 13-Atom Alkali Metal Clusters: Is There an Appropriate Exchange-Correlation Functional?

Density functional theory (DFT) is a treatment widely employed for exploring the electronic structure of atoms, molecules, solids, and complex systems. Despite its efficiency and popularity, the accuracy of DFT results is highly dependent on the choice of exchange–correlation (XC) functionals. This study evaluates several XC functionals for calculating atomization energies in 13-atom homo- and heteronuclear alkali metal clusters (X₁₃ and YX₁₂, with X, Y = Li, Na, K, Rb, and Cs), comparing these results with reference data obtained from fixed-node Diffusion Monte Carlo (DMC) simulations. Our findings emphasize the critical role of the correlation functional in achieving more accurate results. Moreover, empirical dispersion corrections are shown to be quite important for these systems. Notably, PBE and PBE0 functionals with D3-BJ dispersion seem particularly reliable for atomization energy calculations in these clusters.