The atomization energy of Mg4

The atomization energy of Mg4 is determined using the MP2 and CCSD(T) levels of theory. Basis set incompleteness, basis set extrapolation, and core-valence effects are discussed. Our best atomization energy, including the zero-point energy and scalar relativistic effects, is 24.6±1.6 kcal/mol. Our computed and extrapolated values are compared with previous results, where it is observed that our extrapolated MP2 value is in good agreement with the MP2-R12 value. The CCSD(T) and MP2 core effects are found to have the opposite signs.