Interionic Potentials For CaO By The Multiple Lattice Inversion Method

In this work, the lattice inversion was used to obtain the interionic potentials of CaO. In terms of the natural structures of CaO crystals, some virtual structures were introduced, then the pseudopotential total-energy curves as a function of lattice constant were calculated for ionic crystals in different virtual structures. During the calculations, both the equilibrium and non-equilibrium positions have been included, then the phase space as the potential source has been effectively extended to cover more interionic separations and coordination environments. Based on the difference between the long-ranged Coulomb potential and short-ranged interactions, the effective ionic charges were determined from the total-energy difference between the two virtual structures. This avoids using the empirical values as the ionic charges, such as the formal charge, full ionic charge and oxidation charge. Since the Coulomb interaction has been described by the effective ionic charges, the lattice inversion is only used to cope with the short-ranged interionic potentials, then the difficulty for the slow convergence of long-ranged Coulomb potential is totally bypassed. Without the prior potential function forms, the short-range potential curves can be obtained by Chen-M?bius lattice inversion, then the proper potential function forms can be chosen to express the ionic interactions, so the interionic potential curves are basically determined. This avoids several sets of potential parameters and fewer uncertainties will be involved in the derivation of interionic potentials. Since the extended phase space and fewer assumptions are used, the lattice inversion potentials are valid over a wide range of interionic separations and coordination environments. The interionic pair potentials of CaO were obtained by the above lattice inversion. After several tests for the validity of potentials, it is clear that the structural parameters, phase stability, elastic constants, phonon dispersion curves and configurations of CaO clusters have been well reproduced to be in good agreement with the experiment results. This indicates the validity of the inversion pair potentials.Finally, the inversion potentials of SrO and BaO were obtained by different virtual structures in the lattice inversion. This indicates the flexibility of lattice inversion in the derivation of interionic potentials.