Density functional theory calculation of 2p core-electron binding energies of Si, P, S, Cl, and Ar in gas-phase molecules

Density functional theory (DFT) calculations have been performed on the gas-phase 2p core-electron binding energies (CEBEs) of Si, P, S, Cl, and Ar in 145 cases using the following procedure: ΔEKS (scalar-ZORA + Exc)/TZP//HF/6-31G(d). ΔEKS is the difference in the total Kohn-Sham energies of the 2p-ionized cation and the neutral parent molecule calculated by DFT using different exchange-correlation functionals Exc with triple-zeta polarized basis set, at molecular geometry optimized by HF/6-31G(d), and relativistic effects have been estimated by scalar zeroth-order regular approximation. Among the 26 functionals tested, the form of Exc giving the best overall performance was found to be the combination of OPTX exchange and LYP correlation functionals. For that functional, the average absolute deviation (AAD) of the 145 calculated CEBEs from experiment is 0.26 eV. There are seven other exchange-correlation functionals that led to AADs of less than 0.30 eV. Some functionals give lower AADs than Exc = OPTX-LYP for some individual elements. In the case of Si, for example, the combination of either mPW91-PBE or Becke88-Perdew86 led to an AAD of only 0.10 eV for 56 silicon-containing molecules. Another example is the case of the argon atom, for which the choice of Exc = OPTX-Perdew86 yields a value for CEBE equal to the experimental value.