Performance Evaluation on Several Exchange-correlation Functional Ap- proximations in Calculations of Alkali–metals and IB Group Metals Pair Potentials

In the present paper, inter-atomic pair potentials in alkali–metals and IB group metals, in crystal state and diatomic system, respectively, are systematically calculated by means of electronic density functional theory with several exchange-correlation (EC) functional approximations. In the absence of experimental potential function information, experimentally available bonding length and binding energy of crystal lattice structure, and equilibrium separation and potential minimum of diatomic systems, are used for the first time in the context of potential energy as a function of atom separation, to evaluate the performance of the EC approximations considered in calculating the main properties of neutral atom potential energy curve. Comparison between the experiment measures and first-principle calculations indicates that (i) all EC functional approximations show great changes in their performances for different systems, and the performances of a given EC functional approximation are variable even for the same element but different structures. (ii) The EC functional approximations considered show relatively stronger adaptability in calculations for the crystal lattice structures of both alkali-metals and IB metals, but the performances for the IB metals Cu, Ag, Au diatomic systems degrade somewhat; more than that, the alkali-metal Li, Na, K, Rb, and Cs diatomic systems are inexorably the most difficult to be dealt with by all EC approximations considered. (iii) Although the calculated inter-atomic pair potentials in the diatomic system comprised of the IB metals and alkali-metals, respectively, display unmistakable deviations from the experimental measures, they still constitute specific empirical materials on which effective inter-atomic pair potentials are constructed to take into account the three-body interactions in the statistical mechanics theory considering only two-body interactions.